Automated Upgrades

Overview

You can manage K3s cluster upgrades using Rancher’s system-upgrade-controller. This is a Kubernetes-native approach to cluster upgrades. It leverages a custom resource definition (CRD), a plan, and a controller.

The plan defines upgrade policies and requirements. It also defines which nodes should be upgraded through a label selector. See below for plans with defaults appropriate for upgrading a K3s cluster. For more advanced plan configuration options, please review the CRD.

The controller schedules upgrades by monitoring plans and selecting nodes to run upgrade jobs on. When a job has run to completion successfully, the controller will label the node on which it ran accordingly.

The upgrade job that is launched must be highly privileged. It is configured with the following:

  • Host IPC, NET, and PID namespaces

  • The CAP_SYS_BOOT capability

  • Host root mounted at /host with read and write permissions

To automate upgrades in this manner, you must do the following:

  1. Install the system-upgrade-controller into your cluster

  2. Configure plans

If the K3s cluster is managed by Rancher, you should use the Rancher UI to manage upgrades.

  • If the K3s cluster was imported into Rancher, Rancher will manage the system-upgrade-controller deployment and plans. Do not follow the steps on this page.

  • If the K3s cluster was provisioned by Rancher, Rancher will use system agent to manage version upgrades. Do not follow the steps on this page.

  • If the K3s cluster is not managed Rancher, you may follow the steps below.

For more details on the design and architecture of the system-upgrade-controller or its integration with K3s, see the following Git repositories:

When attempting to upgrade to a new version of K3s, the Kubernetes version skew policy applies. Ensure that your plan does not skip intermediate minor versions when upgrading. The system-upgrade-controller itself will not protect against unsupported changes to the Kubernetes version.

Install the system-upgrade-controller

The system-upgrade-controller can be installed as a deployment into your cluster. The deployment requires a service-account, clusterRoleBinding, and a configmap. To install these components, run the following command:

kubectl apply -f https://github.com/rancher/system-upgrade-controller/releases/latest/download/system-upgrade-controller.yaml

The controller can be configured and customized via the previously mentioned configmap, but the controller must be redeployed for the changes to be applied.

To be able to apply plans, the system-upgrade-controller CRD has to be deployed:

kubectl apply -f https://github.com/rancher/system-upgrade-controller/releases/latest/download/crd.yaml

Configure plans

It is recommended you create at least two plans: a plan for upgrading server (control-plane) nodes and a plan for upgrading agent nodes. You can create additional plans as needed to control the rollout of the upgrade across nodes. Once the plans are created, the controller will pick them up and begin to upgrade your cluster.

The following two example plans will upgrade your cluster to K3s v1.24.6+k3s1:

# Server plan
apiVersion: upgrade.cattle.io/v1
kind: Plan
metadata:
  name: server-plan
  namespace: system-upgrade
spec:
  concurrency: 1
  cordon: true
  nodeSelector:
    matchExpressions:
    - key: node-role.kubernetes.io/control-plane
      operator: In
      values:
      - "true"
  serviceAccountName: system-upgrade
  upgrade:
    image: rancher/k3s-upgrade
  version: v1.24.6+k3s1
---
# Agent plan
apiVersion: upgrade.cattle.io/v1
kind: Plan
metadata:
  name: agent-plan
  namespace: system-upgrade
spec:
  concurrency: 1
  cordon: true
  nodeSelector:
    matchExpressions:
    - key: node-role.kubernetes.io/control-plane
      operator: DoesNotExist
  prepare:
    args:
    - prepare
    - server-plan
    image: rancher/k3s-upgrade
  serviceAccountName: system-upgrade
  upgrade:
    image: rancher/k3s-upgrade
  version: v1.24.6+k3s1

There are a few important things to call out regarding these plans:

1) The plans must be created in the same namespace where the controller was deployed.

2) The concurrency field indicates how many nodes can be upgraded at the same time.

3) The server-plan targets server nodes by specifying a label selector that selects nodes with the node-role.kubernetes.io/control-plane label. The agent-plan targets agent nodes by specifying a label selector that select nodes without that label.

4) The prepare step in the agent-plan will cause upgrade jobs for that plan to wait for the server-plan to complete before they execute.

5) Both plans have the version field set to v1.24.6+k3s1. Alternatively, you can omit the version field and set the channel field to a URL that resolves to a release of K3s. This will cause the controller to monitor that URL and upgrade the cluster any time it resolves to a new release. This works well with the release channels. Thus, you can configure your plans with the following channel to ensure your cluster is always automatically upgraded to the newest stable release of K3s:

apiVersion: upgrade.cattle.io/v1
kind: Plan
...
spec:
  ...
  channel: https://update.k3s.io/v1-release/channels/stable

As stated, the upgrade will begin as soon as the controller detects that a plan was created. Updating a plan will cause the controller to re-evaluate the plan and determine if another upgrade is needed.

You can monitor the progress of an upgrade by viewing the plan and jobs via kubectl:

kubectl -n system-upgrade get plans -o yaml
kubectl -n system-upgrade get jobs -o yaml

Downgrade Prevention

Version Gate

Starting with the 2023-07 releases (v1.27.4+k3s1, v1.26.7+k3s1, v1.25.12+k3s1, v1.24.16+k3s1)

Kubernetes does not support downgrades of control-plane components. The k3s-upgrade image used by upgrade plans will refuse to downgrade K3s, failing the plan and leaving your nodes cordoned.

Here is an example cluster, showing failed upgrade pods and cordoned nodes:

ubuntu@user:~$ kubectl get pods -n system-upgrade
NAME                                                              READY   STATUS    RESTARTS   AGE
apply-k3s-server-on-ip-172-31-0-16-with-7af95590a5af8e8c3-2cdc6   0/1     Error     0          9m25s
apply-k3s-server-on-ip-172-31-10-23-with-7af95590a5af8e8c-9xvwg   0/1     Error     0          14m
apply-k3s-server-on-ip-172-31-13-213-with-7af95590a5af8e8-8j72v   0/1     Error     0          18m
system-upgrade-controller-7c4b84d5d9-kkzr6                        1/1     Running   0          20m
ubuntu@user:~$ kubectl get nodes
NAME               STATUS                     ROLES                       AGE   VERSION
ip-172-31-0-16     Ready,SchedulingDisabled   control-plane,etcd,master   19h   v1.27.4+k3s1
ip-172-31-10-23    Ready,SchedulingDisabled   control-plane,etcd,master   19h   v1.27.4+k3s1
ip-172-31-13-213   Ready,SchedulingDisabled   control-plane,etcd,master   19h   v1.27.4+k3s1
ip-172-31-2-13     Ready                      <none>                      19h   v1.27.4+k3s1

You can return your cordoned nodes to service by either of the following methods:

  • Change the version or channel on your plan to target a release that is the same or newer than what is currently running on the cluster, so that the plan succeeds.

  • Delete the plan and manually uncordon the nodes. Use kubectl get plan -n system-upgrade to find the plan name, then kubectl delete plan -n system-upgrade PLAN_NAME to delete it. Once the plan has been deleted, use kubectl uncordon NODE_NAME to uncordon each of the nodes.