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kubeadm Configuration (v1beta3)

Overview

Package v1beta3 defines the v1beta3 version of the kubeadm configuration file format. This version improves on the v1beta2 format by fixing some minor issues and adding a few new fields.

A list of changes since v1beta2:

  • The deprecated "ClusterConfiguration.useHyperKubeImage" field has been removed. Kubeadm no longer supports the hyperkube image.
  • The "ClusterConfiguration.DNS.Type" field has been removed since CoreDNS is the only supported DNS server type by kubeadm.
  • Include "datapolicy" tags on the fields that hold secrets. This would result in the field values to be omitted when API structures are printed with klog.
  • Add "InitConfiguration.SkipPhases", "JoinConfiguration.SkipPhases" to allow skipping a list of phases during kubeadm init/join command execution.
  • Add "InitConfiguration.NodeRegistration.ImagePullPolicy" and "JoinConfiguration.NodeRegistration.ImagePullPolicy" to allow specifying the images pull policy during kubeadm "init" and "join". The value must be one of "Always", "Never" or "IfNotPresent". "IfNotPresent" is the default, which has been the existing behavior prior to this addition.
  • Add "InitConfiguration.Patches.Directory", "JoinConfiguration.Patches.Directory" to allow the user to configure a directory from which to take patches for components deployed by kubeadm.
  • Move the BootstrapToken* API and related utilities out of the "kubeadm" API group to a new group "bootstraptoken". The kubeadm API version v1beta3 no longer contains the BootstrapToken* structures.

Migration from old kubeadm config versions

  • kubeadm v1.15.x and newer can be used to migrate from v1beta1 to v1beta2.
  • kubeadm v1.22.x and newer no longer support v1beta1 and older APIs, but can be used to migrate v1beta2 to v1beta3.

Basics

The preferred way to configure kubeadm is to pass an YAML configuration file with the --config option. Some of the configuration options defined in the kubeadm config file are also available as command line flags, but only the most common/simple use case are supported with this approach.

A kubeadm config file could contain multiple configuration types separated using three dashes (---).

kubeadm supports the following configuration types:

apiVersion: kubeadm.k8s.io/v1beta3
kind: InitConfiguration

apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration

apiVersion: kubelet.config.k8s.io/v1beta1
kind: KubeletConfiguration

apiVersion: kubeproxy.config.k8s.io/v1alpha1
kind: KubeProxyConfiguration

apiVersion: kubeadm.k8s.io/v1beta3
kind: JoinConfiguration

To print the defaults for "init" and "join" actions use the following commands:

kubeadm config print init-defaults
kubeadm config print join-defaults

The list of configuration types that must be included in a configuration file depends by the action you are performing (init or join) and by the configuration options you are going to use (defaults or advanced customization).

If some configuration types are not provided, or provided only partially, kubeadm will use default values; defaults provided by kubeadm includes also enforcing consistency of values across components when required (e.g. --cluster-cidr flag on controller manager and clusterCIDR on kube-proxy).

Users are always allowed to override default values, with the only exception of a small subset of setting with relevance for security (e.g. enforce authorization-mode Node and RBAC on api server)

If the user provides a configuration types that is not expected for the action you are performing, kubeadm will ignore those types and print a warning.

Kubeadm init configuration types

When executing kubeadm init with the --config option, the following configuration types could be used: InitConfiguration, ClusterConfiguration, KubeProxyConfiguration, KubeletConfiguration, but only one between InitConfiguration and ClusterConfiguration is mandatory.

apiVersion: kubeadm.k8s.io/v1beta3
kind: InitConfiguration
bootstrapTokens:
  ...
nodeRegistration:
  ...

The InitConfiguration type should be used to configure runtime settings, that in case of kubeadm init are the configuration of the bootstrap token and all the setting which are specific to the node where kubeadm is executed, including:

  • NodeRegistration, that holds fields that relate to registering the new node to the cluster; use it to customize the node name, the CRI socket to use or any other settings that should apply to this node only (e.g. the node ip).

  • LocalAPIEndpoint, that represents the endpoint of the instance of the API server to be deployed on this node; use it e.g. to customize the API server advertise address.

apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration
networking:
  ...
etcd:
  ...
apiServer:
  extraArgs:
    ...
  extraVolumes:
    ...
...

The ClusterConfiguration type should be used to configure cluster-wide settings, including settings for:

  • networking that holds configuration for the networking topology of the cluster; use it e.g. to customize Pod subnet or services subnet.

  • etcd: use it e.g. to customize the local etcd or to configure the API server for using an external etcd cluster.

  • kube-apiserver, kube-scheduler, kube-controller-manager configurations; use it to customize control-plane components by adding customized setting or overriding kubeadm default settings.

apiVersion: kubeproxy.config.k8s.io/v1alpha1
kind: KubeProxyConfiguration
  ...

The KubeProxyConfiguration type should be used to change the configuration passed to kube-proxy instances deployed in the cluster. If this object is not provided or provided only partially, kubeadm applies defaults.

See https://kubernetes.io/docs/reference/command-line-tools-reference/kube-proxy/ or https://pkg.go.dev/k8s.io/kube-proxy/config/v1alpha1#KubeProxyConfiguration for kube-proxy official documentation.

apiVersion: kubelet.config.k8s.io/v1beta1
kind: KubeletConfiguration
  ...

The KubeletConfiguration type should be used to change the configurations that will be passed to all kubelet instances deployed in the cluster. If this object is not provided or provided only partially, kubeadm applies defaults.

See https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet/ or https://pkg.go.dev/k8s.io/kubelet/config/v1beta1#KubeletConfiguration for kubelet official documentation.

Here is a fully populated example of a single YAML file containing multiple configuration types to be used during a kubeadm init run.

apiVersion: kubeadm.k8s.io/v1beta3
kind: InitConfiguration
bootstrapTokens:
- token: "9a08jv.c0izixklcxtmnze7"
  description: "kubeadm bootstrap token"
  ttl: "24h"
- token: "783bde.3f89s0fje9f38fhf"
  description: "another bootstrap token"
  usages:
  - authentication
  - signing
  groups:
  - system:bootstrappers:kubeadm:default-node-token
nodeRegistration:
  name: "ec2-10-100-0-1"
  criSocket: "/var/run/dockershim.sock"
  taints:
  - key: "kubeadmNode"
    value: "someValue"
    effect: "NoSchedule"
  kubeletExtraArgs:
    v: 4
  ignorePreflightErrors:
    - IsPrivilegedUser
  imagePullPolicy: "IfNotPresent"
localAPIEndpoint:
  advertiseAddress: "10.100.0.1"
  bindPort: 6443
certificateKey: "e6a2eb8581237ab72a4f494f30285ec12a9694d750b9785706a83bfcbbbd2204"
skipPhases:
  - addon/kube-proxy
---
apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration
etcd:
  # one of local or external
  local:
    imageRepository: "k8s.gcr.io"
    imageTag: "3.2.24"
    dataDir: "/var/lib/etcd"
    extraArgs:
      listen-client-urls: "http://10.100.0.1:2379"
    serverCertSANs:
    -  "ec2-10-100-0-1.compute-1.amazonaws.com"
    peerCertSANs:
    - "10.100.0.1"
  # external:
    # endpoints:
    # - "10.100.0.1:2379"
    # - "10.100.0.2:2379"
    # caFile: "/etcd/kubernetes/pki/etcd/etcd-ca.crt"
    # certFile: "/etcd/kubernetes/pki/etcd/etcd.crt"
    # keyFile: "/etcd/kubernetes/pki/etcd/etcd.key"
networking:
  serviceSubnet: "10.96.0.0/16"
  podSubnet: "10.244.0.0/24"
  dnsDomain: "cluster.local"
kubernetesVersion: "v1.21.0"
controlPlaneEndpoint: "10.100.0.1:6443"
apiServer:
  extraArgs:
    authorization-mode: "Node,RBAC"
  extraVolumes:
  - name: "some-volume"
    hostPath: "/etc/some-path"
    mountPath: "/etc/some-pod-path"
    readOnly: false
    pathType: File
  certSANs:
  - "10.100.1.1"
  - "ec2-10-100-0-1.compute-1.amazonaws.com"
  timeoutForControlPlane: 4m0s
controllerManager:
  extraArgs:
    "node-cidr-mask-size": "20"
  extraVolumes:
  - name: "some-volume"
    hostPath: "/etc/some-path"
    mountPath: "/etc/some-pod-path"
    readOnly: false
    pathType: File
scheduler:
  extraArgs:
    address: "10.100.0.1"
  extraVolumes:
  - name: "some-volume"
    hostPath: "/etc/some-path"
    mountPath: "/etc/some-pod-path"
    readOnly: false
    pathType: File
certificatesDir: "/etc/kubernetes/pki"
imageRepository: "k8s.gcr.io"
clusterName: "example-cluster"
---
apiVersion: kubelet.config.k8s.io/v1beta1
kind: KubeletConfiguration
# kubelet specific options here
---
apiVersion: kubeproxy.config.k8s.io/v1alpha1
kind: KubeProxyConfiguration
# kube-proxy specific options here

Kubeadm join configuration types

When executing kubeadm join with the --config option, the JoinConfiguration type should be provided.

apiVersion: kubeadm.k8s.io/v1beta3
kind: JoinConfiguration
  ...

The JoinConfiguration type should be used to configure runtime settings, that in case of kubeadm join are the discovery method used for accessing the cluster info and all the setting which are specific to the node where kubeadm is executed, including:

  • nodeRegistration, that holds fields that relate to registering the new node to the cluster; use it to customize the node name, the CRI socket to use or any other settings that should apply to this node only (e.g. the node ip).

  • apiEndpoint, that represents the endpoint of the instance of the API server to be eventually deployed on this node.

Resource Types

ClusterConfiguration

ClusterConfiguration contains cluster-wide configuration for a kubeadm cluster

FieldDescription
apiVersion
string
kubeadm.k8s.io/v1beta3
kind
string
ClusterConfiguration
etcd
Etcd

etcd holds the configuration for etcd.

networking
Networking

networking holds configuration for the networking topology of the cluster.

kubernetesVersion
string

kubernetesVersion is the target version of the control plane.

controlPlaneEndpoint
string

controlPlaneEndpoint sets a stable IP address or DNS name for the control plane. It can be a valid IP address or a RFC-1123 DNS subdomain, both with optional TCP port. In case the controlPlaneEndpoint is not specified, the advertiseAddress + bindPort are used; in case the controlPlaneEndpoint is specified but without a TCP port, the bindPort is used. Possible usages are:

  • In a cluster with more than one control plane instances, this field should be assigned the address of the external load balancer in front of the control plane instances.
  • In environments with enforced node recycling, the controlPlaneEndpoint could be used for assigning a stable DNS to the control plane.
apiServer
APIServer

apiServer contains extra settings for the API server.

controllerManager
ControlPlaneComponent

controllerManager contains extra settings for the controller manager.

scheduler
ControlPlaneComponent

scheduler contains extra settings for the scheduler.

dns
DNS

dns defines the options for the DNS add-on installed in the cluster.

certificatesDir
string

certificatesDir specifies where to store or look for all required certificates.

imageRepository
string

imageRepository sets the container registry to pull images from. If empty, k8s.gcr.io will be used by default. In case of kubernetes version is a CI build (kubernetes version starts with ci/) gcr.io/k8s-staging-ci-images will be used as a default for control plane components and for kube-proxy, while k8s.gcr.io will be used for all the other images.

featureGates
map[string]bool

featureGates contains the feature gates enabled by the user.

clusterName
string

The cluster name.

InitConfiguration

InitConfiguration contains a list of elements that is specific "kubeadm init"-only runtime information. kubeadm init-only information. These fields are solely used the first time kubeadm init runs. After that, the information in the fields IS NOT uploaded to the kubeadm-config ConfigMap that is used by kubeadm upgrade for instance. These fields must be omitempty.

FieldDescription
apiVersion
string
kubeadm.k8s.io/v1beta3
kind
string
InitConfiguration
bootstrapTokens
[]BootstrapToken

bootstrapTokens is respected at kubeadm init time and describes a set of Bootstrap Tokens to create. This information IS NOT uploaded to the kubeadm cluster configmap, partly because of its sensitive nature

nodeRegistration
NodeRegistrationOptions

nodeRegistration holds fields that relate to registering the new control-plane node to the cluster.

localAPIEndpoint
APIEndpoint

localAPIEndpoint represents the endpoint of the API server instance that's deployed on this control plane node. In HA setups, this differs from ClusterConfiguration.controlPlaneEndpoint in the sense that controlPlaneEndpoint is the global endpoint for the cluster, which then load-balances the requests to each individual API server. This configuration object lets you customize what IP/DNS name and port the local API server advertises it's accessible on. By default, kubeadm tries to auto-detect the IP of the default interface and use that, but in case that process fails you may set the desired value here.

certificateKey
string

certificateKey sets the key with which certificates and keys are encrypted prior to being uploaded in a Secret in the cluster during the uploadcerts init phase.

skipPhases
[]string

skipPhases is a list of phases to skip during command execution. The list of phases can be obtained with the kubeadm init --help command. The flag "--skip-phases" takes precedence over this field.

patches
Patches

patches contains options related to applying patches to components deployed by kubeadm during kubeadm init.

JoinConfiguration

JoinConfiguration contains elements describing a particular node.

FieldDescription
apiVersion
string
kubeadm.k8s.io/v1beta3
kind
string
JoinConfiguration
nodeRegistration
NodeRegistrationOptions

nodeRegistration holds fields that relate to registering the new control-plane node to the cluster.

caCertPath
string

caCertPath is the path to the SSL certificate authority used to secure comunications between a node and the control-plane. Defaults to "/etc/kubernetes/pki/ca.crt".

discovery [Required]
Discovery

discovery specifies the options for the kubelet to use during the TLS bootstrap process.

controlPlane
JoinControlPlane

controlPlane defines the additional control plane instance to be deployed on the joining node. If nil, no additional control plane instance will be deployed.

skipPhases
[]string

skipPhases is a list of phases to skip during command execution. The list of phases can be obtained with the kubeadm join --help command. The flag --skip-phases takes precedence over this field.

patches
Patches

patches contains options related to applying patches to components deployed by kubeadm during kubeadm join.

APIEndpoint

Appears in:

APIEndpoint struct contains elements of API server instance deployed on a node.

FieldDescription
advertiseAddress
string

advertiseAddress sets the IP address for the API server to advertise.

bindPort
int32

bindPort sets the secure port for the API Server to bind to. Defaults to 6443.

APIServer

Appears in:

APIServer holds settings necessary for API server deployments in the cluster

FieldDescription
ControlPlaneComponent [Required]
ControlPlaneComponent
(Members of ControlPlaneComponent are embedded into this type.) No description provided.
certSANs
[]string

certSANs sets extra Subject Alternative Names (SANs) for the API Server signing certificate.

timeoutForControlPlane
meta/v1.Duration

timeoutForControlPlane controls the timeout that we wait for API server to appear.

BootstrapTokenDiscovery

Appears in:

BootstrapTokenDiscovery is used to set the options for bootstrap token based discovery

FieldDescription
token [Required]
string

token is a token used to validate cluster information fetched from the control-plane.

apiServerEndpoint
string

apiServerEndpoint is an IP or domain name to the API server from which information will be fetched.

caCertHashes
[]string

caCertHashes specifies a set of public key pins to verify when token-based discovery is used. The root CA found during discovery must match one of these values. Specifying an empty set disables root CA pinning, which can be unsafe. Each hash is specified as ":", where the only currently supported type is "sha256". This is a hex-encoded SHA-256 hash of the Subject Public Key Info (SPKI) object in DER-encoded ASN.1. These hashes can be calculated using, for example, OpenSSL.

unsafeSkipCAVerification
bool

unsafeSkipCAVerification allows token-based discovery without CA verification via caCertHashes. This can weaken the security of kubeadm since other nodes can impersonate the control-plane.

ControlPlaneComponent

Appears in:

ControlPlaneComponent holds settings common to control plane component of the cluster

FieldDescription
extraArgs
map[string]string

extraArgs is an extra set of flags to pass to the control plane component. A key in this map is the flag name as it appears on the command line except without leading dash(es).

extraVolumes
[]HostPathMount

extraVolumes is an extra set of host volumes, mounted to the control plane component.

DNS

Appears in:

DNS defines the DNS addon that should be used in the cluster

FieldDescription
ImageMeta [Required]
ImageMeta
(Members of ImageMeta are embedded into this type.)

imageMeta allows to customize the image used for the DNS component.

Discovery

Appears in:

Discovery specifies the options for the kubelet to use during the TLS Bootstrap process.

FieldDescription
bootstrapToken
BootstrapTokenDiscovery

bootstrapToken is used to set the options for bootstrap token based discovery. bootstrapToken and file are mutually exclusive.

file
FileDiscovery

file is used to specify a file or URL to a kubeconfig file from which to load cluster information. bootstrapToken and file are mutually exclusive.

tlsBootstrapToken
string

tlsBootstrapToken is a token used for TLS bootstrapping. If bootstrapToken is set, this field is defaulted to .bootstrapToken.token, but can be overridden. If file is set, this field must be set in case the KubeConfigFile does not contain any other authentication information

timeout
meta/v1.Duration

timeout modifies the discovery timeout.

Etcd

Appears in:

Etcd contains elements describing Etcd configuration.

FieldDescription
local
LocalEtcd

local provides configuration knobs for configuring the local etcd instance. local and external are mutually exclusive.

external
ExternalEtcd

external describes how to connect to an external etcd cluster. local and external are mutually exclusive.

ExternalEtcd

Appears in:

ExternalEtcd describes an external etcd cluster. Kubeadm has no knowledge of where certificate files live and they must be supplied.

FieldDescription
endpoints [Required]
[]string

endpoints contains the list of etcd members.

caFile [Required]
string

caFile is an SSL Certificate Authority (CA) file used to secure etcd communication. Required if using a TLS connection.

certFile [Required]
string

certFile is an SSL certification file used to secure etcd communication. Required if using a TLS connection.

keyFile [Required]
string

keyFile is an SSL key file used to secure etcd communication. Required if using a TLS connection.

FileDiscovery

Appears in:

FileDiscovery is used to specify a file or URL to a kubeconfig file from which to load cluster information.

FieldDescription
kubeConfigPath [Required]
string

kubeConfigPath is used to specify the actual file path or URL to the kubeconfig file from which to load cluster information.

HostPathMount

Appears in:

HostPathMount contains elements describing volumes that are mounted from the host.

FieldDescription
name [Required]
string

name is the name of the volume inside the Pod template.

hostPath [Required]
string

hostPath is the path in the host that will be mounted inside the Pod.

mountPath [Required]
string

mountPath is the path inside the Pod where hostPath will be mounted.

readOnly
bool

readOnly controls write access to the volume.

pathType
core/v1.HostPathType

pathType is the type of the hostPath.

ImageMeta

Appears in:

ImageMeta allows to customize the image used for components that are not originated from the Kubernetes/Kubernetes release process

FieldDescription
imageRepository
string

imageRepository sets the container registry to pull images from. If not set, the imageRepository defined in ClusterConfiguration will be used instead.

imageTag
string

imageTag allows to specify a tag for the image. In case this value is set, kubeadm does not change automatically the version of the above components during upgrades.

JoinControlPlane

Appears in:

JoinControlPlane contains elements describing an additional control plane instance to be deployed on the joining node.

FieldDescription
localAPIEndpoint
APIEndpoint

localAPIEndpoint represents the endpoint of the API server instance to be deployed on this node.

certificateKey
string

certificateKey is the key that is used for decryption of certificates after they are downloaded from the secret upon joining a new control plane node. The corresponding encryption key is in the InitConfiguration.

LocalEtcd

Appears in:

LocalEtcd describes that kubeadm should run an etcd cluster locally

FieldDescription
ImageMeta [Required]
ImageMeta
(Members of ImageMeta are embedded into this type.)

ImageMeta allows to customize the container used for etcd.

dataDir [Required]
string

dataDir is the directory etcd will place its data. Defaults to "/var/lib/etcd".

extraArgs
map[string]string

extraArgs are extra arguments provided to the etcd binary when run inside a static Pod. A key in this map is the flag name as it appears on the command line except without leading dash(es).

serverCertSANs
[]string

serverCertSANs sets extra Subject Alternative Names (SANs) for the etcd server signing certificate.

peerCertSANs
[]string

peerCertSANs sets extra Subject Alternative Names (SANs) for the etcd peer signing certificate.

Networking

Appears in:

Networking contains elements describing cluster's networking configuration

FieldDescription
serviceSubnet
string

serviceSubnet is the subnet used by Kubernetes Services. Defaults to "10.96.0.0/12".

podSubnet
string

podSubnet is the subnet used by Pods.

dnsDomain
string

dnsDomain is the DNS domain used by Kubernetes Services. Defaults to "cluster.local".

NodeRegistrationOptions

Appears in:

NodeRegistrationOptions holds fields that relate to registering a new control-plane or node to the cluster, either via "kubeadm init" or "kubeadm join"

FieldDescription
name
string

name is the .metadata.name field of the Node API object that will be created in this kubeadm init or kubeadm join operation. This field is also used in the CommonName field of the kubelet's client certificate to the API server. Defaults to the hostname of the node if not provided.

criSocket
string

criSocket is used to retrieve container runtime info. This information will be annotated to the Node API object, for later re-use

taints [Required]
[]core/v1.Taint

taints specifies the taints the Node API object should be registered with. If this field is unset, i.e. nil, in the kubeadm init process it will be defaulted with a control-plane taint for control-plane nodes. If you don't want to taint your control-plane node, set this field to an empty list, i.e. taints: [] in the YAML file. This field is solely used for Node registration.

kubeletExtraArgs
map[string]string

kubeletExtraArgs passes through extra arguments to the kubelet. The arguments here are passed to the kubelet command line via the environment file kubeadm writes at runtime for the kubelet to source. This overrides the generic base-level configuration in the 'kubelet-config-1.X' ConfigMap. Flags have higher priority when parsing. These values are local and specific to the node kubeadm is executing on. A key in this map is the flag name as it appears on the command line except without leading dash(es).

ignorePreflightErrors
[]string

ignorePreflightErrors provides a list of pre-flight errors to be ignored when the current node is registered.

imagePullPolicy
core/v1.PullPolicy

imagePullPolicy specifies the policy for image pulling during kubeadm "init" and "join" operations. The value of this field must be one of "Always", "IfNotPresent" or "Never". If this field is unset kubeadm will default it to "IfNotPresent", or pull the required images if not present on the host.

Patches

Appears in:

Patches contains options related to applying patches to components deployed by kubeadm.

FieldDescription
directory
string

directory is a path to a directory that contains files named "target[suffix][+patchtype].extension". For example, "kube-apiserver0+merge.yaml" or just "etcd.json". "target" can be one of "kube-apiserver", "kube-controller-manager", "kube-scheduler", "etcd". "patchtype" can be one of "strategic" "merge" or "json" and they match the patch formats supported by kubectl. The default "patchtype" is "strategic". "extension" must be either "json" or "yaml". "suffix" is an optional string that can be used to determine which patches are applied first alpha-numerically.

BootstrapToken

Appears in:

BootstrapToken describes one bootstrap token, stored as a Secret in the cluster

FieldDescription
token [Required]
BootstrapTokenString

token is used for establishing bidirectional trust between nodes and control-planes. Used for joining nodes in the cluster.

description
string

description sets a human-friendly message why this token exists and what it's used for, so other administrators can know its purpose.

ttl
meta/v1.Duration

ttl defines the time to live for this token. Defaults to 24h. expires and ttl are mutually exclusive.

expires
meta/v1.Time

expires specifies the timestamp when this token expires. Defaults to being set dynamically at runtime based on the ttl. expires and ttl are mutually exclusive.

usages
[]string

usages describes the ways in which this token can be used. Can by default be used for establishing bidirectional trust, but that can be changed here.

groups
[]string

groups specifies the extra groups that this token will authenticate as when/if used for authentication

BootstrapTokenString

Appears in:

BootstrapTokenString is a token of the format abcdef.abcdef0123456789 that is used for both validation of the practically of the API server from a joining node's point of view and as an authentication method for the node in the bootstrap phase of "kubeadm join". This token is and should be short-lived.

FieldDescription
- [Required]
string
No description provided.
- [Required]
string
No description provided.
Last modified July 10, 2022 at 5:22 PM PST: Fix spelling typo for taints (6138e0bc67)