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K3S Maintenance

Steps for Updating K3S​

Updating K3S involves safely taking each node offline (one at a time), performing the update, then bringing the node back into the cluster.

Before doing any updates, backup your data. Ensure you have backups of your K3S server data and important configuration files. This is especially crucial if something goes wrong during the update and you need to restore to a previous state.

Draining the Node​

When performing maintenance (such as updating K3S), it’s important to "drain" the node to protect your workloads and avoid interruptions.

What Does "Draining" a Node Mean?​

  • Draining safely evicts all non-essential pods from the node, allowing Kubernetes to reschedule them on other nodes.
  • It also makes the node "unschedulable," ensuring no new pods can be assigned to the node while it’s offline.

What does "evicting" a Pod Mean?​

  • In Kubernetes, "evicts" refers to the process of safely terminating Pods on a node, typically to free up resources or for maintenance, allowing them to be rescheduled on other nodes.

How to Drain a Node:​

To drain a node, run the following command replacing <node-name> with the name of the node you want to update:

kubectl drain <node-name> --ignore-daemonsets --delete-emptydir-data

Explanation of Command Options:

  • --ignore-daemonsets: Prevents Kubernetes from evicting system-critical pods managed by DaemonSets (these won't be touched).
  • --delete-emptydir-data: Deletes any storage associated with EmptyDir volumes (used for temporary data in pods).

Stopping the K3S Service​

To update K3S, we first need to stop the running K3S service on the Raspberry Pi:

sudo systemctl stop k3s

This command stops K3S gracefully, which ensures everything halts correctly and there's no risk of corruption during the update.

Updating K3S​

Now, let's update K3S to its newest version. You can use the official K3S installation script to do this in a streamlined way. Running the script below will automatically detect the current installation and update it to the latest available version:

curl -sfL https://get.k3s.io | sh -

The script will download, install, and configure the latest version of K3S while keeping all your configurations in place.

Starting the K3S Service Again​

Once the update finishes, restart the K3S service on the node to bring it back online:

sudo systemctl start k3s

This will load the new K3S version and all services will resume.

Uncordoning the Node​

What Is "Uncordoning"?​

After an update, we need to make the node available again for scheduling new pods, i.e., undo the "unschedulable" state created during the drain.

How to Uncordon a Node:​

To let Kubernetes know this node is now ready to schedule new pods again:

kubectl uncordon <node-name>

This command marks the node as "schedulable," meaning new pods can now be assigned to it.

Verifying the Update​

Once the node is back online, verify the K3S version to confirm that the update was successful:

k3s --version

Check that the output shows the latest version installed.