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


When joining a kubeadm initialized cluster, we need to establish bidirectional trust. This is split into discovery (having the Node trust the Kubernetes Master) and TLS bootstrap (having the Kubernetes Master 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, 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 Master. The value of this flag is specified as “:”, 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 Master.

The TLS bootstrap mechanism is also driven via a shared token. This is used to temporarily authenticate with the Kubernetes Master to submit a certificate signing request (CSR) for a locally created key pair. By default, kubeadm will set up the Kubernetes Master 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.

kubeadm join [flags]


--apiserver-advertise-address string
If the node should host a new control plane instance, the IP address the API Server will advertise it's listening on.
--apiserver-bind-port int32     Default: 6443
If the node should host a new control plane instance, the port for the API Server to bind to.
--config string
Path to kubeadm config file.
--cri-socket string     Default: "/var/run/dockershim.sock"
Specify the CRI socket to connect to.
--discovery-file string
A file or URL from which to load cluster information.
--discovery-token string
A token used to validate cluster information fetched from the API server.
--discovery-token-ca-cert-hash stringSlice
For token-based discovery, validate that the root CA public key matches this hash (format: "<type>:<value>").
For token-based discovery, allow joining without --discovery-token-ca-cert-hash pinning.
Create a new control plane instance on this node
-h, --help
help for join
--ignore-preflight-errors stringSlice
A list of checks whose errors will be shown as warnings. Example: 'IsPrivilegedUser,Swap'. Value 'all' ignores errors from all checks.
--node-name string
Specify the node name.
--token string
Use this token for both discovery-token and tls-bootstrap-token when those values are not provided.

Options inherited from parent commands

--rootfs string
[EXPERIMENTAL] The path to the 'real' host root filesystem.