This command initializes a Kubernetes control-plane node.
Run this command in order to set up the Kubernetes control plane
Run this command in order to set up the Kubernetes control plane
The “init” command executes the following phases:
preflight Run pre-flight checks
kubelet-start Write kubelet settings and (re)start the kubelet
certs Certificate generation
/etcd-ca Generate the self-signed CA to provision identities for etcd
/apiserver-etcd-client Generate the certificate the apiserver uses to access etcd
/etcd-healthcheck-client Generate the certificate for liveness probes to healtcheck etcd
/etcd-server Generate the certificate for serving etcd
/etcd-peer Generate the certificate for etcd nodes to communicate with each other
/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
/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
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
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]
--apiserver-advertise-address string The IP address the API Server will advertise it's listening on. If not set the default network interface will be used.
--apiserver-bind-port int32 Port for the API Server to bind to. (default 6443)
--apiserver-cert-extra-sans strings Optional extra Subject Alternative Names (SANs) to use for the API Server serving certificate. Can be both IP addresses and DNS names.
--cert-dir string The path where to save and store the certificates. (default "/etc/kubernetes/pki")
--certificate-key string Key used to encrypt the control-plane certificates in the kubeadm-certs Secret.
--config string Path to a kubeadm configuration file.
--cri-socket string Path to the CRI socket to connect. If empty kubeadm will try to auto-detect this value; use this option only if you have more than one CRI installed or if you have non-standard CRI socket.
--dry-run Don't apply any changes; just output what would be done.
--feature-gates string A set of key=value pairs that describe feature gates for various features. No feature gates are available in this release.
-h, --help help for init
--ignore-preflight-errors strings A list of checks whose errors will be shown as warnings. Example: 'IsPrivilegedUser,Swap'. Value 'all' ignores errors from all checks.
--image-repository string Choose a container registry to pull control plane images from (default "k8s.gcr.io")
--kubernetes-version string Choose a specific Kubernetes version for the control plane. (default "stable-1")
--node-name string Specify the node name.
--pod-network-cidr string Specify range of IP addresses for the pod network. If set, the control plane will automatically allocate CIDRs for every node.
--service-cidr string Use alternative range of IP address for service VIPs. (default "10.96.0.0/12")
--service-dns-domain string Use alternative domain for services, e.g. "myorg.internal". (default "cluster.local")
--skip-certificate-key-print Don't print the key used to encrypt the control-plane certificates.
--skip-phases strings List of phases to be skipped
--skip-token-print Skip printing of the default bootstrap token generated by 'kubeadm init'.
--token string The token to use for establishing bidirectional trust between nodes and control-plane nodes. The format is [a-z0-9]{6}\.[a-z0-9]{16} - e.g. abcdef.0123456789abcdef
--token-ttl duration The duration before the token is automatically deleted (e.g. 1s, 2m, 3h). If set to '0', the token will never expire (default 24h0m0s)
--upload-certs Upload control-plane certificates to the kubeadm-certs Secret.
--rootfs string [EXPERIMENTAL] The path to the 'real' host root filesystem.
kubeadm init
bootstraps a Kubernetes control-plane node by executing the
following steps:
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>
.
Generates a self-signed CA (or using an existing one if provided) to set up
identities for each component in the cluster. If the user has provided their
own CA cert and/or key by dropping it in the cert directory configured via --cert-dir
(/etc/kubernetes/pki
by default) this step is skipped as described in the
Using custom certificates document.
The APIServer certs will have additional SAN entries for any --apiserver-cert-extra-sans
arguments, lowercased if necessary.
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
.
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.
Apply labels and taints to the control-plane node so that no additional workloads will run there.
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.
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.
ClusterConfiguration
. For more information about the configuration see the section
Using kubeadm init with a configuration file
below.
Please note that although the DNS server is deployed, it will not be scheduled until CNI is installed.Kubeadm allows you create a control-plane node in phases. In 1.13 the kubeadm init phase
command has graduated to GA from it’s previous alpha state under kubeadm alpha phase
.
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.
Caution: The config file is still considered beta and may change in future versions.
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 in the --config
option.
In Kubernetes 1.11 and later, the default configuration can be printed out using the kubeadm config print command.
It is recommended that you migrate your old v1beta1
configuration to v1beta2
using
the kubeadm config migrate command.
For more details on each field in the v1beta2
configuration you can navigate to our
API reference pages.
For information about kube-proxy parameters in the kubeadm configuration see: - kube-proxy
For information about enabling IPVS mode with kubeadm see: - IPVS
For information about passing flags to control plane components see: - control-plane-flags
By default, kubeadm pulls images from k8s.gcr.io
, unless
the requested Kubernetes version is a CI version. In this case,
gcr.io/kubernetes-ci-images
is used.
You can override this behavior by using kubeadm with a configuration file. Allowed customization are:
imageRepository
to be used instead of
k8s.gcr.io
.useHyperKubeImage
to true
to use the HyperKube image.imageRepository
and imageTag
for etcd or DNS add-on.Please note that the configuration field kubernetesVersion
or the command line flag
--kubernetes-version
affect the version of the images.
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
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 alpha certs certificate-key
By default, kubeadm generates all the certificates needed for a cluster to run. You can override this behavior by providing your own certificates.
To do so, you must place them in whatever directory is specified by the
--cert-dir
flag or CertificatesDir
configuration file key. By default this
is /etc/kubernetes/pki
.
If a given certificate and private key pair exists, kubeadm skips the
generation step and existing files are used for the prescribed
use case. This means you can, for example, copy an existing CA into /etc/kubernetes/pki/ca.crt
and /etc/kubernetes/pki/ca.key
, and kubeadm will use this CA for signing the rest
of the certs.
It is also possible to provide just the ca.crt
file and not the
ca.key
file (this is only available for the root CA file, not other cert pairs).
If all other certificates and kubeconfig files are in place, kubeadm recognizes
this condition and activates the “External CA” mode. kubeadm will proceed without the
CA key on disk.
Instead, run the controller-manager standalone with --controllers=csrsigner
and
point to the CA certificate and key.
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.
Since v1.6.0, Kubernetes has enabled the use of CRI, Container Runtime Interface, by default.
The container runtime used by default is Docker, which is enabled through the built-in
dockershim
CRI implementation inside of the kubelet
.
Other CRI-based runtimes include:
Refer to the CRI installation instructions for more information.
After you have successfully installed kubeadm
and kubelet
, execute
these two additional steps:
Install the runtime shim on every node, following the installation document in the runtime shim project listing above.
Configure kubelet to use the remote CRI runtime. Please remember to change
RUNTIME_ENDPOINT
to your own value like /var/run/{your_runtime}.sock
:
cat > /etc/systemd/system/kubelet.service.d/20-cri.conf <<EOF
[Service]
Environment="KUBELET_EXTRA_ARGS=--container-runtime=remote --container-runtime-endpoint=$RUNTIME_ENDPOINT"
EOF
systemctl daemon-reload
Now kubelet
is ready to use the specified CRI runtime, and you can continue
with the kubeadm init
and kubeadm join
workflow to deploy Kubernetes cluster.
You may also want to set --cri-socket
to kubeadm init
and kubeadm reset
when
using an external CRI implementation.
By default, kubeadm
assigns a node name based on a machine’s host address. You can override this setting with the --node-name
flag.
The flag passes the appropriate --hostname-override
to the kubelet.
Be aware that overriding the hostname can interfere with cloud providers.
For running kubeadm without an internet connection you have to pre-pull the required control-plane images.
In Kubernetes 1.11 and later, you can list and pull the images using the kubeadm config images
sub-command:
kubeadm config images list
kubeadm config images pull
In Kubernetes 1.12 and later, the k8s.gcr.io/kube-*
, k8s.gcr.io/etcd
and k8s.gcr.io/pause
images
don’t require an -${ARCH}
suffix.
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.
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
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
.
Similar can be done for --certificate-key
when joining additional control-plane
nodes. The key can be generated using:
kubeadm alpha 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.
kubeadm init
phaseskubeadm init
or kubeadm join
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