Kubeadm

• 1: Kubeadm Generated
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• 2: kubeadm init
• 3: kubeadm join
• 4: kubeadm upgrade
• 5: kubeadm config
• 6: kubeadm reset
• 7: kubeadm token
• 8: kubeadm version
• 9: kubeadm alpha
• 10: kubeadm certs
• 11: kubeadm init phase
• 12: kubeadm join phase
• 13: kubeadm kubeconfig
• 14: kubeadm reset phase
• 15: kubeadm upgrade phase
• 16: Implementation details

1 - Kubeadm Generated

1.1 -

kubeadm: easily bootstrap a secure Kubernetes cluster

Synopsis

┌──────────────────────────────────────────────────────────┐
│ KUBEADM                                                  │
│ Easily bootstrap a secure Kubernetes cluster             │
│                                                          │
│ Please give us feedback at:                              │
│ https://github.com/kubernetes/kubeadm/issues             │
└──────────────────────────────────────────────────────────┘

Example usage:

Create a two-machine cluster with one control-plane node
(which controls the cluster), and one worker node
(where your workloads, like Pods and Deployments run).

┌──────────────────────────────────────────────────────────┐
│ On the first machine:                                    │
├──────────────────────────────────────────────────────────┤
│ control-plane# kubeadm init                              │
└──────────────────────────────────────────────────────────┘

┌──────────────────────────────────────────────────────────┐
│ On the second machine:                                   │
├──────────────────────────────────────────────────────────┤
│ worker# kubeadm join <arguments-returned-from-init>      │
└──────────────────────────────────────────────────────────┘

You can then repeat the second step on as many other machines as you like.

Options

1.2 -

Commands related to handling kubernetes certificates

Synopsis

Commands related to handling kubernetes certificates

Options

Options inherited from parent commands

1.3 -

Generate certificate keys

Synopsis

This command will print out a secure randomly-generated certificate key that can be used with the "init" command.

You can also use "kubeadm init --upload-certs" without specifying a certificate key and it will generate and print one for you.

kubeadm certs certificate-key [flags]

Options

Options inherited from parent commands

1.4 -

Check certificates expiration for a Kubernetes cluster

Synopsis

Checks expiration for the certificates in the local PKI managed by kubeadm.

kubeadm certs check-expiration [flags]

Options

Options inherited from parent commands

1.5 -

Generate keys and certificate signing requests

Synopsis

Generates keys and certificate signing requests (CSRs) for all the certificates required to run the control plane. This command also generates partial kubeconfig files with private key data in the "users > user > client-key-data" field, and for each kubeconfig file an accompanying ".csr" file is created.

This command is designed for use in Kubeadm External CA Mode. It generates CSRs which you can then submit to your external certificate authority for signing.

The PEM encoded signed certificates should then be saved alongside the key files, using ".crt" as the file extension, or in the case of kubeconfig files, the PEM encoded signed certificate should be base64 encoded and added to the kubeconfig file in the "users > user > client-certificate-data" field.

kubeadm certs generate-csr [flags]

Examples

  # The following command will generate keys and CSRs for all control-plane certificates and kubeconfig files:
  kubeadm certs generate-csr --kubeconfig-dir /tmp/etc-k8s --cert-dir /tmp/etc-k8s/pki

Options

Options inherited from parent commands

1.6 -

Renew certificates for a Kubernetes cluster

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm certs renew [flags]

Options

Options inherited from parent commands

1.7 -

Renew the certificate embedded in the kubeconfig file for the admin to use and for kubeadm itself

Synopsis

Renew the certificate embedded in the kubeconfig file for the admin to use and for kubeadm itself.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew admin.conf [flags]

Options

Options inherited from parent commands

1.8 -

Renew all available certificates

Synopsis

Renew all known certificates necessary to run the control plane. Renewals are run unconditionally, regardless of expiration date. Renewals can also be run individually for more control.

kubeadm certs renew all [flags]

Options

Options inherited from parent commands

1.9 -

Renew the certificate the apiserver uses to access etcd

Synopsis

Renew the certificate the apiserver uses to access etcd.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew apiserver-etcd-client [flags]

Options

Options inherited from parent commands

1.10 -

Renew the certificate for the API server to connect to kubelet

Synopsis

Renew the certificate for the API server to connect to kubelet.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew apiserver-kubelet-client [flags]

Options

Options inherited from parent commands

1.11 -

Renew the certificate for serving the Kubernetes API

Synopsis

Renew the certificate for serving the Kubernetes API.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew apiserver [flags]

Options

Options inherited from parent commands

1.12 -

Renew the certificate embedded in the kubeconfig file for the controller manager to use

Synopsis

Renew the certificate embedded in the kubeconfig file for the controller manager to use.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew controller-manager.conf [flags]

Options

Options inherited from parent commands

1.13 -

Renew the certificate for liveness probes to healthcheck etcd

Synopsis

Renew the certificate for liveness probes to healthcheck etcd.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew etcd-healthcheck-client [flags]

Options

Options inherited from parent commands

1.14 -

Renew the certificate for etcd nodes to communicate with each other

Synopsis

Renew the certificate for etcd nodes to communicate with each other.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew etcd-peer [flags]

Options

Options inherited from parent commands

1.15 -

Renew the certificate for serving etcd

Synopsis

Renew the certificate for serving etcd.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew etcd-server [flags]

Options

Options inherited from parent commands

1.16 -

Renew the certificate for the front proxy client

Synopsis

Renew the certificate for the front proxy client.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew front-proxy-client [flags]

Options

Options inherited from parent commands

1.17 -

Renew the certificate embedded in the kubeconfig file for the scheduler manager to use

Synopsis

Renew the certificate embedded in the kubeconfig file for the scheduler manager to use.

Renewals run unconditionally, regardless of certificate expiration date; extra attributes such as SANs will be based on the existing file/certificates, there is no need to resupply them.

Renewal by default tries to use the certificate authority in the local PKI managed by kubeadm; as alternative it is possible to use K8s certificate API for certificate renewal, or as a last option, to generate a CSR request.

After renewal, in order to make changes effective, is required to restart control-plane components and eventually re-distribute the renewed certificate in case the file is used elsewhere.

kubeadm certs renew scheduler.conf [flags]

Options

Options inherited from parent commands

1.18 -

Output shell completion code for the specified shell (bash or zsh)

Synopsis

Output shell completion code for the specified shell (bash or zsh). The shell code must be evaluated to provide interactive completion of kubeadm commands. This can be done by sourcing it from the .bash_profile.

Note: this requires the bash-completion framework.

To install it on Mac use homebrew: $ brew install bash-completion Once installed, bash_completion must be evaluated. This can be done by adding the following line to the .bash_profile $ source $(brew --prefix)/etc/bash_completion

If bash-completion is not installed on Linux, please install the 'bash-completion' package via your distribution's package manager.

Note for zsh users: [1] zsh completions are only supported in versions of zsh >= 5.2

kubeadm completion SHELL [flags]

Examples

# Install bash completion on a Mac using homebrew
brew install bash-completion
printf "\n# Bash completion support\nsource $(brew --prefix)/etc/bash_completion\n" >> $HOME/.bash_profile
source $HOME/.bash_profile

# Load the kubeadm completion code for bash into the current shell
source <(kubeadm completion bash)

# Write bash completion code to a file and source it from .bash_profile
kubeadm completion bash > ~/.kube/kubeadm_completion.bash.inc
printf "\n# Kubeadm shell completion\nsource '$HOME/.kube/kubeadm_completion.bash.inc'\n" >> $HOME/.bash_profile
source $HOME/.bash_profile

# Load the kubeadm completion code for zsh[1] into the current shell
source <(kubeadm completion zsh)

Options

Options inherited from parent commands

1.19 -

Manage configuration for a kubeadm cluster persisted in a ConfigMap in the cluster

Synopsis

There is a ConfigMap in the kube-system namespace called "kubeadm-config" that kubeadm uses to store internal configuration about the cluster. kubeadm CLI v1.8.0+ automatically creates this ConfigMap with the config used with 'kubeadm init', but if you initialized your cluster using kubeadm v1.7.x or lower, you must use the 'config upload' command to create this ConfigMap. This is required so that 'kubeadm upgrade' can configure your upgraded cluster correctly.

kubeadm config [flags]

Options

Options inherited from parent commands

1.20 -

Interact with container images used by kubeadm

Synopsis

Interact with container images used by kubeadm

kubeadm config images [flags]

Options

Options inherited from parent commands

1.21 -

Print a list of images kubeadm will use. The configuration file is used in case any images or image repositories are customized

Synopsis

Print a list of images kubeadm will use. The configuration file is used in case any images or image repositories are customized

kubeadm config images list [flags]

Options

Options inherited from parent commands

1.22 -

Pull images used by kubeadm

Synopsis

Pull images used by kubeadm

kubeadm config images pull [flags]

Options

Options inherited from parent commands

1.23 -

Read an older version of the kubeadm configuration API types from a file, and output the similar config object for the newer version

Synopsis

This command lets you convert configuration objects of older versions to the latest supported version, locally in the CLI tool without ever touching anything in the cluster. In this version of kubeadm, the following API versions are supported:

• kubeadm.k8s.io/v1beta3

Further, kubeadm can only write out config of version "kubeadm.k8s.io/v1beta3", but read both types. So regardless of what version you pass to the --old-config parameter here, the API object will be read, deserialized, defaulted, converted, validated, and re-serialized when written to stdout or --new-config if specified.

In other words, the output of this command is what kubeadm actually would read internally if you submitted this file to "kubeadm init"

kubeadm config migrate [flags]

Options

Options inherited from parent commands

1.24 -

Print configuration

Synopsis

This command prints configurations for subcommands provided. For details, see: https://pkg.go.dev/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm#section-directories

kubeadm config print [flags]

Options

Options inherited from parent commands

1.25 -

Print default init configuration, that can be used for 'kubeadm init'

Synopsis

This command prints objects such as the default init configuration that is used for 'kubeadm init'.

Note that sensitive values like the Bootstrap Token fields are replaced with placeholder values like "abcdef.0123456789abcdef" in order to pass validation but not perform the real computation for creating a token.

kubeadm config print init-defaults [flags]

Options

Options inherited from parent commands

1.26 -

Print default join configuration, that can be used for 'kubeadm join'

Synopsis

This command prints objects such as the default join configuration that is used for 'kubeadm join'.

Note that sensitive values like the Bootstrap Token fields are replaced with placeholder values like "abcdef.0123456789abcdef" in order to pass validation but not perform the real computation for creating a token.

kubeadm config print join-defaults [flags]

Options

Options inherited from parent commands

1.27 -

Run this command in order to set up the Kubernetes control plane

Synopsis

Run this command in order to set up the Kubernetes control plane

The "init" command executes the following phases:

preflight                    Run pre-flight checks
certs                        Certificate generation
  /ca                          Generate the self-signed Kubernetes CA to provision identities for other Kubernetes components
  /apiserver                   Generate the certificate for serving the Kubernetes API
  /apiserver-kubelet-client    Generate the certificate for the API server to connect to kubelet
  /front-proxy-ca              Generate the self-signed CA to provision identities for front proxy
  /front-proxy-client          Generate the certificate for the front proxy client
  /etcd-ca                     Generate the self-signed CA to provision identities for etcd
  /etcd-server                 Generate the certificate for serving etcd
  /etcd-peer                   Generate the certificate for etcd nodes to communicate with each other
  /etcd-healthcheck-client     Generate the certificate for liveness probes to healthcheck etcd
  /apiserver-etcd-client       Generate the certificate the apiserver uses to access etcd
  /sa                          Generate a private key for signing service account tokens along with its public key
kubeconfig                   Generate all kubeconfig files necessary to establish the control plane and the admin kubeconfig file
  /admin                       Generate a kubeconfig file for the admin to use and for kubeadm itself
  /kubelet                     Generate a kubeconfig file for the kubelet to use *only* for cluster bootstrapping purposes
  /controller-manager          Generate a kubeconfig file for the controller manager to use
  /scheduler                   Generate a kubeconfig file for the scheduler to use
kubelet-start                Write kubelet settings and (re)start the kubelet
control-plane                Generate all static Pod manifest files necessary to establish the control plane
  /apiserver                   Generates the kube-apiserver static Pod manifest
  /controller-manager          Generates the kube-controller-manager static Pod manifest
  /scheduler                   Generates the kube-scheduler static Pod manifest
etcd                         Generate static Pod manifest file for local etcd
  /local                       Generate the static Pod manifest file for a local, single-node local etcd instance
upload-config                Upload the kubeadm and kubelet configuration to a ConfigMap
  /kubeadm                     Upload the kubeadm ClusterConfiguration to a ConfigMap
  /kubelet                     Upload the kubelet component config to a ConfigMap
upload-certs                 Upload certificates to kubeadm-certs
mark-control-plane           Mark a node as a control-plane
bootstrap-token              Generates bootstrap tokens used to join a node to a cluster
kubelet-finalize             Updates settings relevant to the kubelet after TLS bootstrap
  /experimental-cert-rotation  Enable kubelet client certificate rotation
addon                        Install required addons for passing conformance tests
  /coredns                     Install the CoreDNS addon to a Kubernetes cluster
  /kube-proxy                  Install the kube-proxy addon to a Kubernetes cluster

kubeadm init [flags]

Options

Options inherited from parent commands

1.28 -

Use this command to invoke single phase of the init workflow

Synopsis

Use this command to invoke single phase of the init workflow

Options

Options inherited from parent commands

1.29 -

Install required addons for passing conformance tests

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm init phase addon [flags]

Options

Options inherited from parent commands

1.30 -

Install all the addons

Synopsis

Install all the addons

kubeadm init phase addon all [flags]

Options

Options inherited from parent commands

1.31 -

Install the CoreDNS addon to a Kubernetes cluster

Synopsis

Install the CoreDNS addon components via the API server. Please note that although the DNS server is deployed, it will not be scheduled until CNI is installed.

kubeadm init phase addon coredns [flags]

Options

Options inherited from parent commands

1.32 -

Install the kube-proxy addon to a Kubernetes cluster

Synopsis

Install the kube-proxy addon components via the API server.

kubeadm init phase addon kube-proxy [flags]

Options

Options inherited from parent commands

1.33 -

Generates bootstrap tokens used to join a node to a cluster

Synopsis

Bootstrap tokens are used for establishing bidirectional trust between a node joining the cluster and a control-plane node.

This command makes all the configurations required to make bootstrap tokens works and then creates an initial token.

kubeadm init phase bootstrap-token [flags]

Examples

  # Make all the bootstrap token configurations and create an initial token, functionally
  # equivalent to what generated by kubeadm init.
  kubeadm init phase bootstrap-token

Options

Options inherited from parent commands

1.34 -

Certificate generation

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm init phase certs [flags]

Options

Options inherited from parent commands

1.35 -

Generate all certificates

Synopsis

Generate all certificates

kubeadm init phase certs all [flags]

Options

Options inherited from parent commands

1.36 -

Generate the certificate the apiserver uses to access etcd

Synopsis

Generate the certificate the apiserver uses to access etcd, and save them into apiserver-etcd-client.crt and apiserver-etcd-client.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs apiserver-etcd-client [flags]

Options

Options inherited from parent commands

1.37 -

Generate the certificate for the API server to connect to kubelet

Synopsis

Generate the certificate for the API server to connect to kubelet, and save them into apiserver-kubelet-client.crt and apiserver-kubelet-client.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs apiserver-kubelet-client [flags]

Options

Options inherited from parent commands

1.38 -

Generate the certificate for serving the Kubernetes API

Synopsis

Generate the certificate for serving the Kubernetes API, and save them into apiserver.crt and apiserver.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs apiserver [flags]

Options

Options inherited from parent commands

1.39 -

Generate the self-signed Kubernetes CA to provision identities for other Kubernetes components

Synopsis

Generate the self-signed Kubernetes CA to provision identities for other Kubernetes components, and save them into ca.crt and ca.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs ca [flags]

Options

Options inherited from parent commands

1.40 -

Generate the self-signed CA to provision identities for etcd

Synopsis

Generate the self-signed CA to provision identities for etcd, and save them into etcd/ca.crt and etcd/ca.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs etcd-ca [flags]

Options

Options inherited from parent commands

1.41 -

Generate the certificate for liveness probes to healthcheck etcd

Synopsis

Generate the certificate for liveness probes to healthcheck etcd, and save them into etcd/healthcheck-client.crt and etcd/healthcheck-client.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs etcd-healthcheck-client [flags]

Options

Options inherited from parent commands

1.42 -

Generate the certificate for etcd nodes to communicate with each other

Synopsis

Generate the certificate for etcd nodes to communicate with each other, and save them into etcd/peer.crt and etcd/peer.key files.

Default SANs are localhost, 127.0.0.1, 127.0.0.1, ::1

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs etcd-peer [flags]

Options

Options inherited from parent commands

1.43 -

Generate the certificate for serving etcd

Synopsis

Generate the certificate for serving etcd, and save them into etcd/server.crt and etcd/server.key files.

Default SANs are localhost, 127.0.0.1, 127.0.0.1, ::1

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs etcd-server [flags]

Options

Options inherited from parent commands

1.44 -

Generate the self-signed CA to provision identities for front proxy

Synopsis

Generate the self-signed CA to provision identities for front proxy, and save them into front-proxy-ca.crt and front-proxy-ca.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs front-proxy-ca [flags]

Options

Options inherited from parent commands

1.45 -

Generate the certificate for the front proxy client

Synopsis

Generate the certificate for the front proxy client, and save them into front-proxy-client.crt and front-proxy-client.key files.

If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs front-proxy-client [flags]

Options

Options inherited from parent commands

1.46 -

Generate a private key for signing service account tokens along with its public key

Synopsis

Generate the private key for signing service account tokens along with its public key, and save them into sa.key and sa.pub files. If both files already exist, kubeadm skips the generation step and existing files will be used.

Alpha Disclaimer: this command is currently alpha.

kubeadm init phase certs sa [flags]

Options

Options inherited from parent commands

1.47 -

Generate all static Pod manifest files necessary to establish the control plane

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm init phase control-plane [flags]

Options

Options inherited from parent commands

1.48 -

Generate all static Pod manifest files

Synopsis

Generate all static Pod manifest files

kubeadm init phase control-plane all [flags]

Examples

  # Generates all static Pod manifest files for control plane components,
  # functionally equivalent to what is generated by kubeadm init.
  kubeadm init phase control-plane all
  
  # Generates all static Pod manifest files using options read from a configuration file.
  kubeadm init phase control-plane all --config config.yaml

Options

Options inherited from parent commands

1.49 -

Generates the kube-apiserver static Pod manifest

Synopsis

Generates the kube-apiserver static Pod manifest

kubeadm init phase control-plane apiserver [flags]

Options

Options inherited from parent commands

1.50 -

Generates the kube-controller-manager static Pod manifest

Synopsis

Generates the kube-controller-manager static Pod manifest

kubeadm init phase control-plane controller-manager [flags]

Options

Options inherited from parent commands

1.51 -

Generates the kube-scheduler static Pod manifest

Synopsis

Generates the kube-scheduler static Pod manifest

kubeadm init phase control-plane scheduler [flags]

Options

Options inherited from parent commands

1.52 -

Generate static Pod manifest file for local etcd

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm init phase etcd [flags]

Options

Options inherited from parent commands

1.53 -

Generate the static Pod manifest file for a local, single-node local etcd instance

Synopsis

Generate the static Pod manifest file for a local, single-node local etcd instance

kubeadm init phase etcd local [flags]

Examples

  # Generates the static Pod manifest file for etcd, functionally
  # equivalent to what is generated by kubeadm init.
  kubeadm init phase etcd local
  
  # Generates the static Pod manifest file for etcd using options
  # read from a configuration file.
  kubeadm init phase etcd local --config config.yaml

Options

Options inherited from parent commands

1.54 -

Generate all kubeconfig files necessary to establish the control plane and the admin kubeconfig file

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm init phase kubeconfig [flags]

Options

Options inherited from parent commands

1.55 -

Generate a kubeconfig file for the admin to use and for kubeadm itself

Synopsis

Generate the kubeconfig file for the admin and for kubeadm itself, and save it to admin.conf file.

kubeadm init phase kubeconfig admin [flags]

Options

Options inherited from parent commands

1.56 -

Generate all kubeconfig files

Synopsis

Generate all kubeconfig files

kubeadm init phase kubeconfig all [flags]

Options

Options inherited from parent commands

1.57 -

Generate a kubeconfig file for the controller manager to use

Synopsis

Generate the kubeconfig file for the controller manager to use and save it to controller-manager.conf file

kubeadm init phase kubeconfig controller-manager [flags]

Options

Options inherited from parent commands

1.58 -

Generate a kubeconfig file for the kubelet to use only for cluster bootstrapping purposes

Synopsis

Generate the kubeconfig file for the kubelet to use and save it to kubelet.conf file.

Please note that this should only be used for cluster bootstrapping purposes. After your control plane is up, you should request all kubelet credentials from the CSR API.

kubeadm init phase kubeconfig kubelet [flags]

Options

Options inherited from parent commands

1.59 -

Generate a kubeconfig file for the scheduler to use

Synopsis

Generate the kubeconfig file for the scheduler to use and save it to scheduler.conf file.

kubeadm init phase kubeconfig scheduler [flags]

Options

Options inherited from parent commands

1.60 -

Updates settings relevant to the kubelet after TLS bootstrap

Synopsis

Updates settings relevant to the kubelet after TLS bootstrap

kubeadm init phase kubelet-finalize [flags]

Examples

  # Updates settings relevant to the kubelet after TLS bootstrap"
  kubeadm init phase kubelet-finalize all --config

Options

Options inherited from parent commands

1.61 -

Run all kubelet-finalize phases

Synopsis

Run all kubelet-finalize phases

kubeadm init phase kubelet-finalize all [flags]

Examples

  # Updates settings relevant to the kubelet after TLS bootstrap"
  kubeadm init phase kubelet-finalize all --config

Options

Options inherited from parent commands

1.62 -

Enable kubelet client certificate rotation

Synopsis

Enable kubelet client certificate rotation

kubeadm init phase kubelet-finalize experimental-cert-rotation [flags]

Options

Options inherited from parent commands

1.63 -

Write kubelet settings and (re)start the kubelet

Synopsis

Write a file with KubeletConfiguration and an environment file with node specific kubelet settings, and then (re)start kubelet.

kubeadm init phase kubelet-start [flags]

Examples

  # Writes a dynamic environment file with kubelet flags from a InitConfiguration file.
  kubeadm init phase kubelet-start --config config.yaml

Options

Options inherited from parent commands

1.64 -

Mark a node as a control-plane

Synopsis

Mark a node as a control-plane

kubeadm init phase mark-control-plane [flags]

Examples

  # Applies control-plane label and taint to the current node, functionally equivalent to what executed by kubeadm init.
  kubeadm init phase mark-control-plane --config config.yaml
  
  # Applies control-plane label and taint to a specific node
  kubeadm init phase mark-control-plane --node-name myNode

Options

Options inherited from parent commands

1.65 -

Run pre-flight checks

Synopsis

Run pre-flight checks for kubeadm init.

kubeadm init phase preflight [flags]

Examples

  # Run pre-flight checks for kubeadm init using a config file.
  kubeadm init phase preflight --config kubeadm-config.yaml

Options

Options inherited from parent commands

1.66 -

Upload certificates to kubeadm-certs

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm init phase upload-certs [flags]

Options

Options inherited from parent commands

1.67 -

Upload the kubeadm and kubelet configuration to a ConfigMap

Synopsis

This command is not meant to be run on its own. See list of available subcommands.

kubeadm init phase upload-config [flags]

Options

Options inherited from parent commands

1.68 -

Upload all configuration to a config map

Synopsis

Upload all configuration to a config map

kubeadm init phase upload-config all [flags]

Options

Options inherited from parent commands

1.69 -

Upload the kubeadm ClusterConfiguration to a ConfigMap

Synopsis

Upload the kubeadm ClusterConfiguration to a ConfigMap called kubeadm-config in the kube-system namespace. This enables correct configuration of system components and a seamless user experience when upgrading.

Alternatively, you can use kubeadm config.

kubeadm init phase upload-config kubeadm [flags]

Examples

  # upload the configuration of your cluster
  kubeadm init phase upload-config --config=myConfig.yaml

Options

Options inherited from parent commands

1.70 -

Upload the kubelet component config to a ConfigMap

Synopsis

Upload the kubelet configuration extracted from the kubeadm InitConfiguration object to a kubelet-config ConfigMap in the cluster

kubeadm init phase upload-config kubelet [flags]

Examples

  # Upload the kubelet configuration from the kubeadm Config file to a ConfigMap in the cluster.
  kubeadm init phase upload-config kubelet --config kubeadm.yaml

Options

Options inherited from parent commands

1.71 -

Run this on any machine you wish to join an existing cluster

Synopsis

When joining a kubeadm initialized cluster, we need to establish bidirectional trust. This is split into discovery (having the Node trust the Kubernetes Control Plane) and TLS bootstrap (having the Kubernetes Control Plane trust the Node).

There are 2 main schemes for discovery. The first is to use a shared token along with the IP address of the API server. The second is to provide a file - a subset of the standard kubeconfig file. This file can be a local file or downloaded via an HTTPS URL. The forms are kubeadm join --discovery-token abcdef.1234567890abcdef 1.2.3.4:6443, kubeadm join --discovery-file path/to/file.conf, or kubeadm join --discovery-file https://url/file.conf. Only one form can be used. If the discovery information is loaded from a URL, HTTPS must be used. Also, in that case the host installed CA bundle is used to verify the connection.

If you use a shared token for discovery, you should also pass the --discovery-token-ca-cert-hash flag to validate the public key of the root certificate authority (CA) presented by the Kubernetes Control Plane. The value of this flag is specified as "<hash-type>:<hex-encoded-value>", where the supported hash type is "sha256". The hash is calculated over the bytes of the Subject Public Key Info (SPKI) object (as in RFC7469). This value is available in the output of "kubeadm init" or can be calculated using standard tools. The --discovery-token-ca-cert-hash flag may be repeated multiple times to allow more than one public key.

If you cannot know the CA public key hash ahead of time, you can pass the --discovery-token-unsafe-skip-ca-verification flag to disable this verification. This weakens the kubeadm security model since other nodes can potentially impersonate the Kubernetes Control Plane.

The TLS bootstrap mechanism is also driven via a shared token. This is used to temporarily authenticate with the Kubernetes Control Plane to submit a certificate signing request (CSR) for a locally created key pair. By default, kubeadm will set up the Kubernetes Control Plane to automatically approve these signing requests. This token is passed in with the --tls-bootstrap-token abcdef.1234567890abcdef flag.

Often times the same token is used for both parts. In this case, the --token flag can be used instead of specifying each token individually.

The "join [api-server-endpoint]" command executes the following phases:

preflight              Run join pre-flight checks
control-plane-prepare  Prepare the machine for serving a control plane
  /download-certs        [EXPERIMENTAL] Download certificates shared among control-plane nodes from the kubeadm-certs Secret
  /certs                 Generate the certificates for the new control plane components
  /kubeconfig            Generate the kubeconfig for the new control plane components
  /control-plane         Generate the manifests for the new control plane components
kubelet-start          Write kubelet settings, certificates and (re)start the kubelet
control-plane-join     Join a machine as a control plane instance
  /etcd                  Add a new local etcd member
  /update-status         Register the new control-plane node into the ClusterStatus maintained in the kubeadm-config ConfigMap (DEPRECATED)
  /mark-control-plane    Mark a node as a control-plane

kubeadm join [api-server-endpoint] [flags]

Options

Options inherited from parent commands

1.72 -

Use this command to invoke single phase of the join workflow

Synopsis

Use this command to invoke single phase of the join workflow

Options

Options inherited from parent commands

1.73 -

Join a machine as a control plane instance

Synopsis

Join a machine as a control plane instance

kubeadm join phase control-plane-join [flags]

Examples

  # Joins a machine as a control plane instance
  kubeadm join phase control-plane-join all

Options

Options inherited from parent commands

1.74 -

Join a machine as a control plane instance

Synopsis

Join a machine as a control plane instance

kubeadm join phase control-plane-join all [flags]

Options

Options inherited from parent commands

1.75 -

Add a new local etcd member

Synopsis

Add a new local etcd member

kubeadm join phase control-plane-join etcd [flags]

Options

Options inherited from parent commands

1.76 -

Mark a node as a control-plane

Synopsis

Mark a node as a control-plane

kubeadm join phase control-plane-join mark-control-plane [flags]

Options

Options inherited from parent commands

1.77 -

Register the new control-plane node into the ClusterStatus maintained in the kubeadm-config ConfigMap (DEPRECATED)

Synopsis

Register the new control-plane node into the ClusterStatus maintained in the kubeadm-config ConfigMap (DEPRECATED)

kubeadm join phase control-plane-join update-status [flags]

Options

Options inherited from parent commands

1.78 -

Prepare the machine for serving a control plane

Synopsis

Prepare the machine for serving a control plane

kubeadm join phase control-plane-prepare [flags]

Examples

  # Prepares the machine for serving a control plane
  kubeadm join phase control-plane-prepare all

Options

Options inherited from parent commands

1.79 -

Prepare the machine for serving a control plane

Synopsis

Prepare the machine for serving a control plane

kubeadm join phase control-plane-prepare all [api-server-endpoint] [flags]

Options

Options inherited from parent commands

1.80 -

Generate the certificates for the new control plane components

Synopsis

Generate the certificates for the new control plane components

kubeadm join phase control-plane-prepare certs [api-server-endpoint] [flags]

Options

Options inherited from parent commands

1.81 -

Generate the manifests for the new control plane components

Synopsis

Generate the manifests for the new control plane components

kubeadm join phase control-plane-prepare control-plane [flags]

Options

Options inherited from parent commands

1.82 -

[EXPERIMENTAL] Download certificates shared among control-plane nodes from the kubeadm-certs Secret

Synopsis

[EXPERIMENTAL] Download certificates shared among control-plane nodes from the kubeadm-certs Secret

kubeadm join phase control-plane-prepare download-certs [api-server-endpoint] [flags]

Options

Options inherited from parent commands

1.83 -

Generate the kubeconfig for the new control plane components

Synopsis

Generate the kubeconfig for the new control plane components

kubeadm join phase control-plane-prepare kubeconfig [api-server-endpoint] [flags]

Options

Options inherited from parent commands

1.84 -

Write kubelet settings, certificates and (re)start the kubelet

Synopsis

Write a file with KubeletConfiguration and an environment file with node specific kubelet settings, and then (re)start kubelet.

kubeadm join phase kubelet-start [api-server-endpoint] [flags]

Options

Options inherited from parent commands

1.85 -

Run join pre-flight checks

Synopsis

Run pre-flight checks for kubeadm join.

kubeadm join phase preflight [api-server-endpoint] [flags]

Examples

  # Run join pre-flight checks using a config file.
  kubeadm join phase preflight --config kubeadm-config.yaml

Options

Options inherited from parent commands

1.86 -

Kubeconfig file utilities

Synopsis

Kubeconfig file utilities.

Options

Options inherited from parent commands

1.87 -

Output a kubeconfig file for an additional user

Synopsis

Output a kubeconfig file for an additional user.

kubeadm kubeconfig user [flags]

Examples

  # Output a kubeconfig file for an additional user named foo using a kubeadm config file bar
  kubeadm kubeconfig user --client-name=foo --config=bar

Options

Options inherited from parent commands

1.88 -

Performs a best effort revert of changes made to this host by 'kubeadm init' or 'kubeadm join'

Synopsis

Performs a best effort revert of changes made to this host by 'kubeadm init' or 'kubeadm join'

The "reset" command executes the following phases:

preflight           Run reset pre-flight checks
remove-etcd-member  Remove a local etcd member.
cleanup-node        Run cleanup node.

kubeadm reset [flags]

Options

Options inherited from parent commands

1.89 -

Use this command to invoke single phase of the reset workflow

Synopsis

Use this command to invoke single phase of the reset workflow

Options

Options inherited from parent commands

1.90 -

Run cleanup node.

Synopsis

Run cleanup node.

kubeadm reset phase cleanup-node [flags]

Options

Options inherited from parent commands

1.91 -

Run reset pre-flight checks

Synopsis

Run pre-flight checks for kubeadm reset.

kubeadm reset phase preflight [flags]

Options

Options inherited from parent commands

1.92 -

Remove a local etcd member.

Synopsis

Remove a local etcd member for a control plane node.

kubeadm reset phase remove-etcd-member [flags]

Options

Options inherited from parent commands

1.93 -

Manage bootstrap tokens

Synopsis

This command manages bootstrap tokens. It is optional and needed only for advanced use cases.

In short, bootstrap tokens are used for establishing bidirectional trust between a client and a server. A bootstrap token can be used when a client (for example a node that is about to join the cluster) needs to trust the server it is talking to. Then a bootstrap token with the "signing" usage can be used. bootstrap tokens can also function as a way to allow short-lived authentication to the API Server (the token serves as a way for the API Server to trust the client), for example for doing the TLS Bootstrap.

What is a bootstrap token more exactly?

• It is a Secret in the kube-system namespace of type "bootstrap.kubernetes.io/token".
• A bootstrap token must be of the form "[a-z0-9]{6}.[a-z0-9]{16}". The former part is the public token ID, while the latter is the Token Secret and it must be kept private at all circumstances!
• The name of the Secret must be named "bootstrap-token-(token-id)".

You can read more about bootstrap tokens here: https://kubernetes.io/docs/admin/bootstrap-tokens/

kubeadm token [flags]

Options

Options inherited from parent commands

1.94 -

Create bootstrap tokens on the server

Synopsis

This command will create a bootstrap token for you. You can specify the usages for this token, the "time to live" and an optional human friendly description.

The [token] is the actual token to write. This should be a securely generated random token of the form "[a-z0-9]{6}.[a-z0-9]{16}". If no [token] is given, kubeadm will generate a random token instead.

kubeadm token create [token]

Options

Options inherited from parent commands

1.95 -

Delete bootstrap tokens on the server

Synopsis

This command will delete a list of bootstrap tokens for you.

The [token-value] is the full Token of the form "[a-z0-9]{6}.[a-z0-9]{16}" or the Token ID of the form "[a-z0-9]{6}" to delete.

kubeadm token delete [token-value] ...

Options

Options inherited from parent commands

1.96 -

Generate and print a bootstrap token, but do not create it on the server

Synopsis

This command will print out a randomly-generated bootstrap token that can be used with the "init" and "join" commands.

You don't have to use this command in order to generate a token. You can do so yourself as long as it is in the format "[a-z0-9]{6}.[a-z0-9]{16}". This command is provided for convenience to generate tokens in the given format.

You can also use "kubeadm init" without specifying a token and it will generate and print one for you.

kubeadm token generate [flags]

Options

Options inherited from parent commands

1.97 -

List bootstrap tokens on the server

Synopsis

This command will list all bootstrap tokens for you.

kubeadm token list [flags]

Options

Options inherited from parent commands

1.98 -

Upgrade your cluster smoothly to a newer version with this command

Synopsis

Upgrade your cluster smoothly to a newer version with this command

kubeadm upgrade [flags]

Options

Options inherited from parent commands

1.99 -

Upgrade your Kubernetes cluster to the specified version

Synopsis

Upgrade your Kubernetes cluster to the specified version

kubeadm upgrade apply [version]

Options

Options inherited from parent commands

1.100 -

Show what differences would be applied to existing static pod manifests. See also: kubeadm upgrade apply --dry-run

Synopsis

Show what differences would be applied to existing static pod manifests. See also: kubeadm upgrade apply --dry-run

kubeadm upgrade diff [version] [flags]

Options

Options inherited from parent commands

1.101 -

Upgrade commands for a node in the cluster

Synopsis

Upgrade commands for a node in the cluster

The "node" command executes the following phases:

preflight       Run upgrade node pre-flight checks
control-plane   Upgrade the control plane instance deployed on this node, if any
kubelet-config  Upgrade the kubelet configuration for this node

kubeadm upgrade node [flags]

Options

Options inherited from parent commands

1.102 -

Use this command to invoke single phase of the node workflow

Synopsis

Use this command to invoke single phase of the node workflow

Options

Options inherited from parent commands

1.103 -

Upgrade the control plane instance deployed on this node, if any

Synopsis

Upgrade the control plane instance deployed on this node, if any

kubeadm upgrade node phase control-plane [flags]

Options

Options inherited from parent commands

1.104 -

Upgrade the kubelet configuration for this node

Synopsis

Download the kubelet configuration from the kubelet-config ConfigMap stored in the cluster

kubeadm upgrade node phase kubelet-config [flags]

Options

Options inherited from parent commands

1.105 -

Run upgrade node pre-flight checks

Synopsis

Run pre-flight checks for kubeadm upgrade node.

kubeadm upgrade node phase preflight [flags]

Options

Options inherited from parent commands

1.106 -

Check which versions are available to upgrade to and validate whether your current cluster is upgradeable. To skip the internet check, pass in the optional [version] parameter

Synopsis

Check which versions are available to upgrade to and validate whether your current cluster is upgradeable. To skip the internet check, pass in the optional [version] parameter

kubeadm upgrade plan [version] [flags]

Options

Options inherited from parent commands

1.107 -

Print the version of kubeadm

Synopsis

Print the version of kubeadm

kubeadm version [flags]

Options

Options inherited from parent commands

1.108 -

All files in this directory are auto-generated from other repos. Do not edit them manually. You must edit them in their upstream repo.

2 - kubeadm init

This command initializes a Kubernetes control-plane node.

Run this command in order to set up the Kubernetes control plane

Synopsis

Run this command in order to set up the Kubernetes control plane

The "init" command executes the following phases:

preflight                    Run pre-flight checks
certs                        Certificate generation
  /ca                          Generate the self-signed Kubernetes CA to provision identities for other Kubernetes components
  /apiserver                   Generate the certificate for serving the Kubernetes API
  /apiserver-kubelet-client    Generate the certificate for the API server to connect to kubelet
  /front-proxy-ca              Generate the self-signed CA to provision identities for front proxy
  /front-proxy-client          Generate the certificate for the front proxy client
  /etcd-ca                     Generate the self-signed CA to provision identities for etcd
  /etcd-server                 Generate the certificate for serving etcd
  /etcd-peer                   Generate the certificate for etcd nodes to communicate with each other
  /etcd-healthcheck-client     Generate the certificate for liveness probes to healthcheck etcd
  /apiserver-etcd-client       Generate the certificate the apiserver uses to access etcd
  /sa                          Generate a private key for signing service account tokens along with its public key
kubeconfig                   Generate all kubeconfig files necessary to establish the control plane and the admin kubeconfig file
  /admin                       Generate a kubeconfig file for the admin to use and for kubeadm itself
  /kubelet                     Generate a kubeconfig file for the kubelet to use *only* for cluster bootstrapping purposes
  /controller-manager          Generate a kubeconfig file for the controller manager to use
  /scheduler                   Generate a kubeconfig file for the scheduler to use
kubelet-start                Write kubelet settings and (re)start the kubelet
control-plane                Generate all static Pod manifest files necessary to establish the control plane
  /apiserver                   Generates the kube-apiserver static Pod manifest
  /controller-manager          Generates the kube-controller-manager static Pod manifest
  /scheduler                   Generates the kube-scheduler static Pod manifest
etcd                         Generate static Pod manifest file for local etcd
  /local                       Generate the static Pod manifest file for a local, single-node local etcd instance
upload-config                Upload the kubeadm and kubelet configuration to a ConfigMap
  /kubeadm                     Upload the kubeadm ClusterConfiguration to a ConfigMap
  /kubelet                     Upload the kubelet component config to a ConfigMap
upload-certs                 Upload certificates to kubeadm-certs
mark-control-plane           Mark a node as a control-plane
bootstrap-token              Generates bootstrap tokens used to join a node to a cluster
kubelet-finalize             Updates settings relevant to the kubelet after TLS bootstrap
  /experimental-cert-rotation  Enable kubelet client certificate rotation
addon                        Install required addons for passing conformance tests
  /coredns                     Install the CoreDNS addon to a Kubernetes cluster
  /kube-proxy                  Install the kube-proxy addon to a Kubernetes cluster

kubeadm init [flags]

Options

Options inherited from parent commands

Init workflow

kubeadm init bootstraps a Kubernetes control-plane node by executing the following steps:

1. Runs a series of pre-flight checks to validate the system state before making changes. Some checks only trigger warnings, others are considered errors and will exit kubeadm until the problem is corrected or the user specifies --ignore-preflight-errors=<list-of-errors>.

2. Generates a self-signed CA to set up identities for each component in the cluster. The user can provide their own CA cert and/or key by dropping it in the cert directory configured via --cert-dir (/etc/kubernetes/pki by default). The APIServer certs will have additional SAN entries for any --apiserver-cert-extra-sans arguments, lowercased if necessary.

3. Writes kubeconfig files in /etc/kubernetes/ for the kubelet, the controller-manager and the scheduler to use to connect to the API server, each with its own identity, as well as an additional kubeconfig file for administration named admin.conf.

4. Generates static Pod manifests for the API server, controller-manager and scheduler. In case an external etcd is not provided, an additional static Pod manifest is generated for etcd.

   Static Pod manifests are written to /etc/kubernetes/manifests; the kubelet watches this directory for Pods to create on startup.

   Once control plane Pods are up and running, the kubeadm init sequence can continue.

5. Apply labels and taints to the control-plane node so that no additional workloads will run there.

6. Generates the token that additional nodes can use to register themselves with a control-plane in the future. Optionally, the user can provide a token via --token, as described in the kubeadm token docs.

7. Makes all the necessary configurations for allowing node joining with the Bootstrap Tokens and TLS Bootstrap mechanism:

   • Write a ConfigMap for making available all the information required for joining, and set up related RBAC access rules.

   • Let Bootstrap Tokens access the CSR signing API.

   • Configure auto-approval for new CSR requests.

   See kubeadm join for additional info.

8. Installs a DNS server (CoreDNS) and the kube-proxy addon components via the API server. In Kubernetes version 1.11 and later CoreDNS is the default DNS server. Please note that although the DNS server is deployed, it will not be scheduled until CNI is installed.

   Warning: kube-dns usage with kubeadm is deprecated as of v1.18 and is removed in v1.21.

Using init phases with kubeadm

Kubeadm allows you to create a control-plane node in phases using the kubeadm init phase command.

To view the ordered list of phases and sub-phases you can call kubeadm init --help. The list will be located at the top of the help screen and each phase will have a description next to it. Note that by calling kubeadm init all of the phases and sub-phases will be executed in this exact order.

Some phases have unique flags, so if you want to have a look at the list of available options add --help, for example:

sudo kubeadm init phase control-plane controller-manager --help

You can also use --help to see the list of sub-phases for a certain parent phase:

sudo kubeadm init phase control-plane --help

kubeadm init also exposes a flag called --skip-phases that can be used to skip certain phases. The flag accepts a list of phase names and the names can be taken from the above ordered list.

An example:

sudo kubeadm init phase control-plane all --config=configfile.yaml
sudo kubeadm init phase etcd local --config=configfile.yaml
# you can now modify the control plane and etcd manifest files
sudo kubeadm init --skip-phases=control-plane,etcd --config=configfile.yaml

What this example would do is write the manifest files for the control plane and etcd in /etc/kubernetes/manifests based on the configuration in configfile.yaml. This allows you to modify the files and then skip these phases using --skip-phases. By calling the last command you will create a control plane node with the custom manifest files.

Alternatively, you can use the skipPhases field under InitConfiguration.

Using kubeadm init with a configuration file

It's possible to configure kubeadm init with a configuration file instead of command line flags, and some more advanced features may only be available as configuration file options. This file is passed using the --config flag and it must contain a ClusterConfiguration structure and optionally more structures separated by ---\n Mixing --config with others flags may not be allowed in some cases.

The default configuration can be printed out using the kubeadm config print command.

If your configuration is not using the latest version it is recommended that you migrate using the kubeadm config migrate command.

For more information on the fields and usage of the configuration you can navigate to our API reference page.

Using kubeadm init with feature gates

Kubeadm supports a set of feature gates that are unique to kubeadm and can only be applied during cluster creation with kubeadm init. These features can control the behavior of the cluster. Feature gates are removed after a feature graduates to GA.

To pass a feature gate you can either use the --feature-gates flag for kubeadm init, or you can add items into the featureGates field when you pass a configuration file using --config.

Passing feature gates for core Kubernetes components directly to kubeadm is not supported. Instead, it is possible to pass them by Customizing components with the kubeadm API.

List of feature gates:

Feature gate descriptions:

PublicKeysECDSA

Can be used to create a cluster that uses ECDSA certificates instead of the default RSA algorithm. Renewal of existing ECDSA certificates is also supported using kubeadm certs renew, but you cannot switch between the RSA and ECDSA algorithms on the fly or during upgrades.

RootlessControlPlane

Setting this flag configures the kubeadm deployed control plane component static Pod containers for kube-apiserver, kube-controller-manager, kube-scheduler and etcd to run as non-root users. If the flag is not set, those components run as root. You can change the value of this feature gate before you upgrade to a newer version of Kubernetes.

UnversionedKubeletConfigMap

This flag controls the name of the ConfigMap where kubeadm stores kubelet configuration data. With this flag not specified or set to true, the ConfigMap is named kubelet-config. If you set this flag to false, the name of the ConfigMap includes the major and minor version for Kubernetes (for example: kubelet-config-1.24). Kubeadm ensures that RBAC rules for reading and writing that ConfigMap are appropriate for the value you set. When kubeadm writes this ConfigMap (during kubeadm init or kubeadm upgrade apply), kubeadm respects the value of UnversionedKubeletConfigMap. When reading that ConfigMap (during kubeadm join, kubeadm reset, kubeadm upgrade ...), kubeadm attempts to use unversioned ConfigMap name first; if that does not succeed, kubeadm falls back to using the legacy (versioned) name for that ConfigMap.

Adding kube-proxy parameters

For information about kube-proxy parameters in the kubeadm configuration see:

• kube-proxy reference

For information about enabling IPVS mode with kubeadm see:

• IPVS

Passing custom flags to control plane components

For information about passing flags to control plane components see:

• control-plane-flags

Running kubeadm without an Internet connection

For running kubeadm without an Internet connection you have to pre-pull the required control-plane images.

You can list and pull the images using the kubeadm config images sub-command:

kubeadm config images list
kubeadm config images pull

You can pass --config to the above commands with a kubeadm configuration file to control the kubernetesVersion and imageRepository fields.

All default k8s.gcr.io images that kubeadm requires support multiple architectures.

Using custom images

By default, kubeadm pulls images from k8s.gcr.io. If the requested Kubernetes version is a CI label (such as ci/latest) gcr.io/k8s-staging-ci-images is used.

You can override this behavior by using kubeadm with a configuration file. Allowed customization are:

• To provide kubernetesVersion which affects the version of the images.
• To provide an alternative imageRepository to be used instead of k8s.gcr.io.
• To provide a specific imageRepository and imageTag for etcd or CoreDNS.

Image paths between the default k8s.gcr.io and a custom repository specified using imageRepository may differ for backwards compatibility reasons. For example, one image might have a subpath at k8s.gcr.io/subpath/image, but be defaulted to my.customrepository.io/image when using a custom repository.

To ensure you push the images to your custom repository in paths that kubeadm can consume, you must:

• Pull images from the defaults paths at k8s.gcr.io using kubeadm config images {list|pull}.
• Push images to the paths from kubeadm config images list --config=config.yaml, where config.yaml contains the custom imageRepository, and/or imageTag for etcd and CoreDNS.
• Pass the same config.yaml to kubeadm init.

Uploading control-plane certificates to the cluster

By adding the flag --upload-certs to kubeadm init you can temporary upload the control-plane certificates to a Secret in the cluster. Please note that this Secret will expire automatically after 2 hours. The certificates are encrypted using a 32byte key that can be specified using --certificate-key. The same key can be used to download the certificates when additional control-plane nodes are joining, by passing --control-plane and --certificate-key to kubeadm join.

The following phase command can be used to re-upload the certificates after expiration:

kubeadm init phase upload-certs --upload-certs --certificate-key=SOME_VALUE --config=SOME_YAML_FILE

If the flag --certificate-key is not passed to kubeadm init and kubeadm init phase upload-certs a new key will be generated automatically.

The following command can be used to generate a new key on demand:

kubeadm certs certificate-key

Certificate management with kubeadm

For detailed information on certificate management with kubeadm see Certificate Management with kubeadm. The document includes information about using external CA, custom certificates and certificate renewal.

Managing the kubeadm drop-in file for the kubelet

The kubeadm package ships with a configuration file for running the kubelet by systemd. Note that the kubeadm CLI never touches this drop-in file. This drop-in file is part of the kubeadm DEB/RPM package.

For further information, see Managing the kubeadm drop-in file for systemd.

Use kubeadm with CRI runtimes

By default kubeadm attempts to detect your container runtime. For more details on this detection, see the kubeadm CRI installation guide.

Setting the node name

By default, kubeadm assigns a node name based on a machine's host address. You can override this setting with the --node-name flag. The flag passes the appropriate --hostname-override value to the kubelet.

Be aware that overriding the hostname can interfere with cloud providers.

Automating kubeadm

Rather than copying the token you obtained from kubeadm init to each node, as in the basic kubeadm tutorial, you can parallelize the token distribution for easier automation. To implement this automation, you must know the IP address that the control-plane node will have after it is started, or use a DNS name or an address of a load balancer.

1. Generate a token. This token must have the form <6 character string>.<16 character string>. More formally, it must match the regex: [a-z0-9]{6}\.[a-z0-9]{16}.

   kubeadm can generate a token for you:

    kubeadm token generate
   

2. Start both the control-plane node and the worker nodes concurrently with this token. As they come up they should find each other and form the cluster. The same --token argument can be used on both kubeadm init and kubeadm join.

3. Similar can be done for --certificate-key when joining additional control-plane nodes. The key can be generated using:

   kubeadm certs certificate-key
   

Once the cluster is up, you can grab the admin credentials from the control-plane node at /etc/kubernetes/admin.conf and use that to talk to the cluster.

Note that this style of bootstrap has some relaxed security guarantees because it does not allow the root CA hash to be validated with --discovery-token-ca-cert-hash (since it's not generated when the nodes are provisioned). For details, see the kubeadm join.

What's next

• kubeadm init phase to understand more about kubeadm init phases
• kubeadm join to bootstrap a Kubernetes worker node and join it to the cluster
• kubeadm upgrade to upgrade a Kubernetes cluster to a newer version
• kubeadm reset to revert any changes made to this host by kubeadm init or kubeadm join

3 - kubeadm join

This command initializes a Kubernetes worker node and joins it to the cluster.

Run this on any machine you wish to join an existing cluster

Synopsis

When joining a kubeadm initialized cluster, we need to establish bidirectional trust. This is split into discovery (having the Node trust the Kubernetes Control Plane) and TLS bootstrap (having the Kubernetes Control Plane trust the Node).

There are 2 main schemes for discovery. The first is to use a shared token along with the IP address of the API server. The second is to provide a file - a subset of the standard kubeconfig file. This file can be a local file or downloaded via an HTTPS URL. The forms are kubeadm join --discovery-token abcdef.1234567890abcdef 1.2.3.4:6443, kubeadm join --discovery-file path/to/file.conf, or kubeadm join --discovery-file https://url/file.conf. Only one form can be used. If the discovery information is loaded from a URL, HTTPS must be used. Also, in that case the host installed CA bundle is used to verify the connection.

If you use a shared token for discovery, you should also pass the --discovery-token-ca-cert-hash flag to validate the public key of the root certificate authority (CA) presented by the Kubernetes Control Plane. The value of this flag is specified as "<hash-type>:<hex-encoded-value>", where the supported hash type is "sha256". The hash is calculated over the bytes of the Subject Public Key Info (SPKI) object (as in RFC7469). This value is available in the output of "kubeadm init" or can be calculated using standard tools. The --discovery-token-ca-cert-hash flag may be repeated multiple times to allow more than one public key.

If you cannot know the CA public key hash ahead of time, you can pass the --discovery-token-unsafe-skip-ca-verification flag to disable this verification. This weakens the kubeadm security model since other nodes can potentially impersonate the Kubernetes Control Plane.

The TLS bootstrap mechanism is also driven via a shared token. This is used to temporarily authenticate with the Kubernetes Control Plane to submit a certificate signing request (CSR) for a locally created key pair. By default, kubeadm will set up the Kubernetes Control Plane to automatically approve these signing requests. This token is passed in with the --tls-bootstrap-token abcdef.1234567890abcdef flag.

Often times the same token is used for both parts. In this case, the --token flag can be used instead of specifying each token individually.

The "join [api-server-endpoint]" command executes the following phases:

preflight              Run join pre-flight checks
control-plane-prepare  Prepare the machine for serving a control plane
  /download-certs        [EXPERIMENTAL] Download certificates shared among control-plane nodes from the kubeadm-certs Secret
  /certs                 Generate the certificates for the new control plane components
  /kubeconfig            Generate the kubeconfig for the new control plane components
  /control-plane         Generate the manifests for the new control plane components
kubelet-start          Write kubelet settings, certificates and (re)start the kubelet
control-plane-join     Join a machine as a control plane instance
  /etcd                  Add a new local etcd member
  /update-status         Register the new control-plane node into the ClusterStatus maintained in the kubeadm-config ConfigMap (DEPRECATED)
  /mark-control-plane    Mark a node as a control-plane

kubeadm join [api-server-endpoint] [flags]

Options

Options inherited from parent commands

The join workflow

kubeadm join bootstraps a Kubernetes worker node or a control-plane node and adds it to the cluster. This action consists of the following steps for worker nodes:

1. kubeadm downloads necessary cluster information from the API server. By default, it uses the bootstrap token and the CA key hash to verify the authenticity of that data. The root CA can also be discovered directly via a file or URL.

2. Once the cluster information is known, kubelet can start the TLS bootstrapping process.

   The TLS bootstrap uses the shared token to temporarily authenticate with the Kubernetes API server to submit a certificate signing request (CSR); by default the control plane signs this CSR request automatically.

3. Finally, kubeadm configures the local kubelet to connect to the API server with the definitive identity assigned to the node.

For control-plane nodes additional steps are performed:

1. Downloading certificates shared among control-plane nodes from the cluster (if explicitly requested by the user).

2. Generating control-plane component manifests, certificates and kubeconfig.

3. Adding new local etcd member.

Using join phases with kubeadm

Kubeadm allows you join a node to the cluster in phases using kubeadm join phase.

To view the ordered list of phases and sub-phases you can call kubeadm join --help. The list will be located at the top of the help screen and each phase will have a description next to it. Note that by calling kubeadm join all of the phases and sub-phases will be executed in this exact order.

Some phases have unique flags, so if you want to have a look at the list of available options add --help, for example:

kubeadm join phase kubelet-start --help

Similar to the kubeadm init phase command, kubeadm join phase allows you to skip a list of phases using the --skip-phases flag.

For example:

sudo kubeadm join --skip-phases=preflight --config=config.yaml

Alternatively, you can use the skipPhases field in JoinConfiguration.

Discovering what cluster CA to trust

The kubeadm discovery has several options, each with security tradeoffs. The right method for your environment depends on how you provision nodes and the security expectations you have about your network and node lifecycles.

Token-based discovery with CA pinning

This is the default mode in kubeadm. In this mode, kubeadm downloads the cluster configuration (including root CA) and validates it using the token as well as validating that the root CA public key matches the provided hash and that the API server certificate is valid under the root CA.

The CA key hash has the format sha256:<hex_encoded_hash>. By default, the hash value is returned in the kubeadm join command printed at the end of kubeadm init or in the output of kubeadm token create --print-join-command. It is in a standard format (see RFC7469) and can also be calculated by 3rd party tools or provisioning systems. For example, using the OpenSSL CLI:

openssl x509 -pubkey -in /etc/kubernetes/pki/ca.crt | openssl rsa -pubin -outform der 2>/dev/null | openssl dgst -sha256 -hex | sed 's/^.* //'

Example kubeadm join commands:

For worker nodes:

kubeadm join --discovery-token abcdef.1234567890abcdef --discovery-token-ca-cert-hash sha256:1234..cdef 1.2.3.4:6443

For control-plane nodes:

kubeadm join --discovery-token abcdef.1234567890abcdef --discovery-token-ca-cert-hash sha256:1234..cdef --control-plane 1.2.3.4:6443

You can also call join for a control-plane node with --certificate-key to copy certificates to this node, if the kubeadm init command was called with --upload-certs.

Advantages:

• Allows bootstrapping nodes to securely discover a root of trust for the control-plane node even if other worker nodes or the network are compromised.

• Convenient to execute manually since all of the information required fits into a single kubeadm join command.

Disadvantages:

• The CA hash is not normally known until the control-plane node has been provisioned, which can make it more difficult to build automated provisioning tools that use kubeadm. By generating your CA in beforehand, you may workaround this limitation.

Token-based discovery without CA pinning

This mode relies only on the symmetric token to sign (HMAC-SHA256) the discovery information that establishes the root of trust for the control-plane. To use the mode the joining nodes must skip the hash validation of the CA public key, using --discovery-token-unsafe-skip-ca-verification. You should consider using one of the other modes if possible.

Example kubeadm join command:

kubeadm join --token abcdef.1234567890abcdef --discovery-token-unsafe-skip-ca-verification 1.2.3.4:6443

Advantages:

• Still protects against many network-level attacks.

• The token can be generated ahead of time and shared with the control-plane node and worker nodes, which can then bootstrap in parallel without coordination. This allows it to be used in many provisioning scenarios.

Disadvantages:

• If an attacker is able to steal a bootstrap token via some vulnerability, they can use that token (along with network-level access) to impersonate the control-plane node to other bootstrapping nodes. This may or may not be an appropriate tradeoff in your environment.

File or HTTPS-based discovery

This provides an out-of-band way to establish a root of trust between the control-plane node and bootstrapping nodes. Consider using this mode if you are building automated provisioning using kubeadm. The format of the discovery file is a regular Kubernetes kubeconfig file.

In case the discovery file does not contain credentials, the TLS discovery token will be used.

Example kubeadm join commands:

• kubeadm join --discovery-file path/to/file.conf (local file)

• kubeadm join --discovery-file https://url/file.conf (remote HTTPS URL)

Advantages:

• Allows bootstrapping nodes to securely discover a root of trust for the control-plane node even if the network or other worker nodes are compromised.

Disadvantages:

• Requires that you have some way to carry the discovery information from the control-plane node to the bootstrapping nodes. If the discovery file contains credentials you must keep it secret and transfer it over a secure channel. This might be possible with your cloud provider or provisioning tool.

Securing your installation even more

The defaults for kubeadm may not work for everyone. This section documents how to tighten up a kubeadm installation at the cost of some usability.

Turning off auto-approval of node client certificates

By default, there is a CSR auto-approver enabled that basically approves any client certificate request for a kubelet when a Bootstrap Token was used when authenticating. If you don't want the cluster to automatically approve kubelet client certs, you can turn it off by executing this command:

kubectl delete clusterrolebinding kubeadm:node-autoapprove-bootstrap

After that, kubeadm join will block until the admin has manually approved the CSR in flight:

kubectl get csr

The output is similar to this:

NAME                                                   AGE       REQUESTOR                 CONDITION
node-csr-c69HXe7aYcqkS1bKmH4faEnHAWxn6i2bHZ2mD04jZyQ   18s       system:bootstrap:878f07   Pending

kubectl certificate approve node-csr-c69HXe7aYcqkS1bKmH4faEnHAWxn6i2bHZ2mD04jZyQ

The output is similar to this:

certificatesigningrequest "node-csr-c69HXe7aYcqkS1bKmH4faEnHAWxn6i2bHZ2mD04jZyQ" approved

kubectl get csr

The output is similar to this:

NAME                                                   AGE       REQUESTOR                 CONDITION
node-csr-c69HXe7aYcqkS1bKmH4faEnHAWxn6i2bHZ2mD04jZyQ   1m        system:bootstrap:878f07   Approved,Issued

This forces the workflow that kubeadm join will only succeed if kubectl certificate approve has been run.

Turning off public access to the cluster-info ConfigMap

In order to achieve the joining flow using the token as the only piece of validation information, a ConfigMap with some data needed for validation of the control-plane node's identity is exposed publicly by default. While there is no private data in this ConfigMap, some users might wish to turn it off regardless. Doing so will disable the ability to use the --discovery-token flag of the kubeadm join flow. Here are the steps to do so:

• Fetch the cluster-info file from the API Server:

kubectl -n kube-public get cm cluster-info -o yaml | grep "kubeconfig:" -A11 | grep "apiVersion" -A10 | sed "s/    //" | tee cluster-info.yaml

The output is similar to this:

apiVersion: v1
kind: Config
clusters:
- cluster:
    certificate-authority-data: <ca-cert>
    server: https://<ip>:<port>
  name: ""
contexts: []
current-context: ""
preferences: {}
users: []

• Use the cluster-info.yaml file as an argument to kubeadm join --discovery-file.

• Turn off public access to the cluster-info ConfigMap:

kubectl -n kube-public delete rolebinding kubeadm:bootstrap-signer-clusterinfo

These commands should be run after kubeadm init but before kubeadm join.

Using kubeadm join with a configuration file

It's possible to configure kubeadm join with a configuration file instead of command line flags, and some more advanced features may only be available as configuration file options. This file is passed using the --config flag and it must contain a JoinConfiguration structure. Mixing --config with others flags may not be allowed in some cases.

The default configuration can be printed out using the kubeadm config print command.

If your configuration is not using the latest version it is recommended that you migrate using the kubeadm config migrate command.

For more information on the fields and usage of the configuration you can navigate to our API reference.

What's next

• kubeadm init to bootstrap a Kubernetes control-plane node
• kubeadm token to manage tokens for kubeadm join
• kubeadm reset to revert any changes made to this host by kubeadm init or kubeadm join

4 - kubeadm upgrade

kubeadm upgrade is a user-friendly command that wraps complex upgrading logic behind one command, with support for both planning an upgrade and actually performing it.

kubeadm upgrade guidance

The steps for performing an upgrade using kubeadm are outlined in this document. For older versions of kubeadm, please refer to older documentation sets of the Kubernetes website.

You can use kubeadm upgrade diff to see the changes that would be applied to static pod manifests.

In Kubernetes v1.15.0 and later, kubeadm upgrade apply and kubeadm upgrade node will also automatically renew the kubeadm managed certificates on this node, including those stored in kubeconfig files. To opt-out, it is possible to pass the flag --certificate-renewal=false. For more details about certificate renewal see the certificate management documentation.

kubeadm upgrade plan

Check which versions are available to upgrade to and validate whether your current cluster is upgradeable. To skip the internet check, pass in the optional [version] parameter

Synopsis

Check which versions are available to upgrade to and validate whether your current cluster is upgradeable. To skip the internet check, pass in the optional [version] parameter

kubeadm upgrade plan [version] [flags]

Options

Options inherited from parent commands

kubeadm upgrade apply

Upgrade your Kubernetes cluster to the specified version

Synopsis

Upgrade your Kubernetes cluster to the specified version

kubeadm upgrade apply [version]

Options

Options inherited from parent commands

kubeadm upgrade diff

Show what differences would be applied to existing static pod manifests. See also: kubeadm upgrade apply --dry-run

Synopsis

Show what differences would be applied to existing static pod manifests. See also: kubeadm upgrade apply --dry-run

kubeadm upgrade diff [version] [flags]

Options

Options inherited from parent commands

kubeadm upgrade node

Upgrade commands for a node in the cluster

Synopsis

Upgrade commands for a node in the cluster

The "node" command executes the following phases:

preflight       Run upgrade node pre-flight checks
control-plane   Upgrade the control plane instance deployed on this node, if any
kubelet-config  Upgrade the kubelet configuration for this node

kubeadm upgrade node [flags]

Options

Options inherited from parent commands

What's next

• kubeadm config if you initialized your cluster using kubeadm v1.7.x or lower, to configure your cluster for kubeadm upgrade

5 - kubeadm config

During kubeadm init, kubeadm uploads the ClusterConfiguration object to your cluster in a ConfigMap called kubeadm-config in the kube-system namespace. This configuration is then read during kubeadm join, kubeadm reset and kubeadm upgrade.

You can use kubeadm config print to print the default static configuration that kubeadm uses for kubeadm init and kubeadm join.

For more information on init and join navigate to Using kubeadm init with a configuration file or Using kubeadm join with a configuration file.

For more information on using the kubeadm configuration API navigate to Customizing components with the kubeadm API.

You can use kubeadm config migrate to convert your old configuration files that contain a deprecated API version to a newer, supported API version.

kubeadm config images list and kubeadm config images pull can be used to list and pull the images that kubeadm requires.

kubeadm config print

Print configuration

Synopsis

This command prints configurations for subcommands provided. For details, see: https://pkg.go.dev/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm#section-directories

kubeadm config print [flags]

Options

Options inherited from parent commands

kubeadm config print init-defaults

Print default init configuration, that can be used for 'kubeadm init'

Synopsis

This command prints objects such as the default init configuration that is used for 'kubeadm init'.

Note that sensitive values like the Bootstrap Token fields are replaced with placeholder values like "abcdef.0123456789abcdef" in order to pass validation but not perform the real computation for creating a token.

kubeadm config print init-defaults [flags]

Options

Options inherited from parent commands

kubeadm config print join-defaults

Print default join configuration, that can be used for 'kubeadm join'

Synopsis

This command prints objects such as the default join configuration that is used for 'kubeadm join'.

Note that sensitive values like the Bootstrap Token fields are replaced with placeholder values like "abcdef.0123456789abcdef" in order to pass validation but not perform the real computation for creating a token.

kubeadm config print join-defaults [flags]

Options

Options inherited from parent commands

kubeadm config migrate

Read an older version of the kubeadm configuration API types from a file, and output the similar config object for the newer version

Synopsis

This command lets you convert configuration objects of older versions to the latest supported version, locally in the CLI tool without ever touching anything in the cluster. In this version of kubeadm, the following API versions are supported:

• kubeadm.k8s.io/v1beta3

Further, kubeadm can only write out config of version "kubeadm.k8s.io/v1beta3", but read both types. So regardless of what version you pass to the --old-config parameter here, the API object will be read, deserialized, defaulted, converted, validated, and re-serialized when written to stdout or --new-config if specified.

In other words, the output of this command is what kubeadm actually would read internally if you submitted this file to "kubeadm init"

kubeadm config migrate [flags]

Options

Options inherited from parent commands

kubeadm config images list

Print a list of images kubeadm will use. The configuration file is used in case any images or image repositories are customized

Synopsis

Print a list of images kubeadm will use. The configuration file is used in case any images or image repositories are customized

kubeadm config images list [flags]

Options

Options inherited from parent commands

kubeadm config images pull

Pull images used by kubeadm

Synopsis

Pull images used by kubeadm

kubeadm config images pull [flags]

Options