Add the maintenance procedure

docs/maintenance.md

@@ -0,0 +1,49 @@
+# Maintenance
+
+## How to update supported Kubernetes
+
+Meows supports the three latest Kubernetes versions.
+If a new Kubernetes version is released, please update the followings:
+
+### 1. Update supported kubernetes and dependencies versions
+
+- Kubernetes versions: You can check the versions at <https://hub.docker.com/r/kindest/node/tags>.
+  - `k8s-version` in [.github/workflows/main.yaml](/.github/workflows/main.yaml)
+  - "Supported software" in [README.md](/README.md)
+- Tools versions:
+  - Update `CONTROLLER_GEN_VERSION` in [Makefile](/Makefile) to the latest version from <https://github.com/kubernetes-sigs/controller-tools/releases>.
+  - Update `RUNNER_VERSION` in [Dockerfile](/Dockerfile) to the latest version from <https://github.com/actions/runner/releases>.
+  - In [kindtest/Makefile](/kindtest/Makefile):
+    - Update `KINDTEST_K8S_VERSION` to the latest supported version of kubernetes.
+    - Update `KUSTOMIZE_VERSION` to the latest version from <https://github.com/kubernetes-sigs/kustomize/releases>.
+    - Update `KIND_VERSION` to the latest version from <https://github.com/kubernetes-sigs/kind/releases>.
+    - Update `CERT_MANAGER_VERSION` to the latest version from <https://github.com/cert-manager/cert-manager/releases>.
+- After saving the changes above, update `ENVTEST_K8S_VERSION` in [Makefile](/Makefile) to the latest patch version among the latest supported kubernetes minor versions listed by running `make setup && tmp/bin/setup-envtest list` at the root of this repository. If the latest minor supported version is `1.30.Z`, find `1.30.Z+` from the output but not `1.31.Z`.
+- Other dependencies versions:
+  - Update `ghcr.io/cybozu/golang` image in [Dockerfile](/Dockerfile) to the latest version from <https://github.com/cybozu/neco-containers/pkgs/container/golang>.
+- `go.mod` and `go.sum`:
+  - Run `go get -u ./...`.
+
+If Kubernetes or controller-runtime API has changed, please update the relevant source code accordingly.
+
+### 2. Update meows by running `make`
+
+You can update meows by running the following `make` commands:
+
+```sh
+make setup
+make manifests
+make build
+```
+
+### 3. Fix test code if tests fail
+
+After pushing the change, if the CI fails, fix the tests and push the changes again.
+
+_e.g._, <https://github.com/cybozu-go/meows/pull/185>
+
+### 4. Release the new version
+
+After merging the changes above, follow the procedures written in [Release.md](/RELEASE.md) and release the new version.
+
+_e.g._, <https://github.com/cybozu-go/meows/pull/186>