constellation/.github/docs/upgrade-kubernetes.md

# Upgrading Kubernetes

Constellation is a Kubernetes distribution. As such, dependencies on Kubernetes versions exist in multiple places:

- The desired Kubernetes version deployed by `kubeadm init`
- Kubernetes resources (deployments made while initializing Kubernetes, including the `cloud-controller-manager`, `cluster-autoscaler` and more)
- Kubernetes go dependencies for the bootstrapper code

## Understand what has changed

Before adding support for a new Kubernetes version, it is a very good idea to [read the release notes](https://kubernetes.io/releases/notes/) and to identify breaking changes.

## Upgrading Kubernetes resources

Everything related to Kubernetes versions is tracked in [the versions file](/internal/versions/versions.go). Add a new `ValidK8sVersion` and fill out the `VersionConfigs` entry for that version.
During cluster initialization, multiple Kubernetes resources are deployed. Some of these should be upgraded with Kubernetes.
You can check available version tags for container images using [the container registry tags API](https://docs.docker.com/registry/spec/api/#listing-image-tags):

```sh
curl -q https://k8s.gcr.io/v2/autoscaling/cluster-autoscaler/tags/list | jq .tags
curl -q https://k8s.gcr.io/v2/cloud-controller-manager/tags/list | jq .tags
curl -q https://us.gcr.io/v2/k8s-artifacts-prod/provider-aws/cloud-controller-manager/tags/list | jq .tags
curl -q https://mcr.microsoft.com/v2/oss/kubernetes/azure-cloud-controller-manager/tags/list | jq .tags
curl -q https://mcr.microsoft.com/v2/oss/kubernetes/azure-cloud-node-manager/tags/list | jq .tags
# [...]
```

## Upgrade go dependencies

The [`go.mod`](/go.mod) and [`go.sum`](/go.sum) files pin versions of the Kubernetes go packages. While these do not need to be on the exact versions used in the Kubernetes deployment, it is a good idea to keep them updated and on a similar version.
Upgrade Kubernetes go dependencies by changing the versions of all packages in the `k8s.io` namespace from the old version to the new version in [`go.mod`](/go.mod) and run `go mod tidy`. Ensure that there are no other conflicts and test your changes.
See the diff of [this PR](https://github.com/edgelesssys/constellation/pull/110) as an example of updating the go dependencies.

## Test the new Kubernetes version

- Setup a Constellation cluster using the new image with the new bootstrapper binary and check if Kubernetes is deployed successfully.

    ```sh
    # should print the new k8s version for every node
    kubectl get nodes -o wide
    # read the logs for pods deployed in the kube-system namespace and ensure they are healthy
    kubectl -n kube-system get pods
    kubectl -n kube-system logs [...]
    kubectl -n kube-system describe pods
    ```

- Read the logs of the main Kubernetes components by getting a shell on the nodes and scan for errors / deprecation warnings:

    ```sh
    journalctl -u kubelet
    journalctl -u containerd
    ```

- Conduct e2e tests
  - [Run the sonobuoy test suite against your branch](https://sonobuoy.io/)
  - [Run CI e2e tests](/.github/docs/README.md)