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[EXPERIMENTAL] Extending a K2s Cluster

This guide explains how to extend a K2s cluster by adding physical hosts or virtual machines to an existing K2s setup.

Prerequisites

  1. K2s Installed Machine:
  2. Ensure the existing machine with K2s installed is accessible.

  3. Confirm that the K2s cluster is running and healthy.

  4. New Host or VM Requirements:

  5. Install a compatible operating system (Linux or Windows, based on your cluster requirements).
  6. Install an SSH service on the new machine and ensure port 22 is enabled for connectivity.
  7. Ensure network connectivity with the K2s node.
  8. IP Address Requirements:
    • The IP address of the new machine must be in the same subnet as the K2s setup (e.g., 172.94.91.0/24).

Known Limitations

  • Adding a new node works only if there is an internet connection on the new node. (Offline support is in progress.)
  • Adding a new physical host is currently supported only on Debian and Ubuntu Linux distributions.

Steps to Add a Physical Host or VM

1. Copy the public SSH Key to the new node

When K2s is installed, an SSH public key is available under the directory %USERPROFILE%\.ssh\kubemaster\id_rsa.pub. This key must be copied to the physical host or VM to establish communication and initiate the installation.

Manually

Copy the file from %USERPROFILE%\.ssh\kubemaster\id_rsa.pub to any location on the machine e.g. /tmp/ on Linux host .

Using scp and password

Linux New Node
Text Only
scp -o StrictHostKeyChecking=no %USERPROFILE%\.ssh\kubemaster\id_rsa.pub  <usernameOfNode>@<IpAddressOfNode>:/tmp/temp_k2s.pub
Windows New Node
Text Only
scp -o StrictHostKeyChecking=no %USERPROFILE%\.ssh\kubemaster\id_rsa.pub  <usernameOfNode>@<IpAddressOfNode>:c:\\temp\\temp_k2s.pub

scp

Typically the password will be requested for the user to complete scp operation.

2. Add copied public SSH Key to the Authorized Users Key File of SSH Service

This operation ensures that the new node can be connected over SSH from K2s setup.

On Linux New Node

Text Only
cat /tmp/temp_k2s.pub >> ~/.ssh/authorized_keys && cat ~/.ssh/authorized_keys

On Windows New Node

PowerShell
$rootPublicKey = 'c:\temp\temp_k2s.pub'
$authorizedkeypath = 'C:\ProgramData\ssh\administrators_authorized_keys'

Write-Output 'Adding public key for SSH connection'

if ((Test-Path $authorizedkeypath -PathType Leaf)) {
    Write-Output "$authorizedkeypath already exists! overwriting new key"

    Set-Content $authorizedkeypath -Value $rootPublicKey
}
else {
    New-Item $authorizedkeypath -ItemType File -Value $rootPublicKey

    $acl = Get-Acl C:\ProgramData\ssh\administrators_authorized_keys
    $acl.SetAccessRuleProtection($true, $false)
    $administratorsRule = New-Object system.security.accesscontrol.filesystemaccessrule('Administrators', 'FullControl', 'Allow')
    $systemRule = New-Object system.security.accesscontrol.filesystemaccessrule('SYSTEM', 'FullControl', 'Allow')
    $acl.SetAccessRule($administratorsRule)
    $acl.SetAccessRule($systemRule)
    $acl | Set-Acl
}

3. Add new node with K2s CLI

Text Only
k2s node add --ip-addr <IPAddressOfNewNode> --username <UserNameForRemoteConnection>

4. Check new node status

Text Only
k2s status -o wide