Automatically manage pre-release branches

We need to automatically create k8s-snap branches for upstream
pre-releases such as v1.33.0-alpha.1.

Whenever a new pre-release or stable release comes out, the old
pre-release branches become obsolete and are automatically
removed.

Note that these branches are used by the Launchpad recipes to
produce and publish k8s-snap builds.

.github/workflows/update-branches.yaml → .github/workflows/update-flavor-branches.yaml

@@ -1,4 +1,4 @@
-name: Auto-update branches
+name: Auto-update flavor branches
 
 on:
   push:
@@ -45,3 +45,4 @@ jobs:
       - name: Push to ${{ steps.determine.outputs.branch }}
         run: |
           git push origin --force ${{ steps.determine.outputs.branch }}
+ 

.github/workflows/update-pre-release-branches.yaml

@@ -0,0 +1,63 @@
+name: Auto-update pre-release branches
+
+on:
+  push:
+    branches:
+      - main
+  schedule:
+    - cron: "0 0 * * *" # Runs every midnight
+
+permissions:
+  contents: read
+
+jobs:
+  update-branches:
+    permissions:
+      contents: write  # for Git to git push
+    runs-on: ubuntu-latest
+    outputs:
+      preRelease: ${{ steps.determine.outputs.preRelease }}
+      branch: ${{ steps.determine.outputs.branch }}
+    steps:
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+      - name: Install Python dependencies
+        run: pip3 install packaging requests
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          ssh-key: ${{ secrets.BOT_SSH_KEY }}
+      - name: Determine outstanding pre-release
+        id: determine
+        run: |
+          preRelease=`python3 ./build-scripts/k8s_releases.py get_outstanding_prerelease`
+          echo "preRelease=$preRelease" >> "$GITHUB_OUTPUT"
+
+          if [[ -n "$preRelease" ]]; then
+            branch="autoupdate/$preRelease"
+          fi
+          echo "branch=$branch" >> "$GITHUB_OUTPUT"
+      - name: Create pre-release branch ${{ steps.determine.outputs.branch }}
+        if: ${{ steps.determine.outputs.preRelease }} != ''
+        run: |
+          git checkout -b ${{ steps.determine.outputs.branch }}
+          git push origin --force ${{ steps.determine.outputs.branch }}
+      - name: Clean obsolete branches
+        run: |
+          git fetch origin
+
+          # Log the latest release for reference.
+          latestRelease=`python3 ./build-scripts/k8s_releases.py get_latest_release`
+          echo "Latest k8s release: $latestRelease"
+
+          for outstandingPreRelease in `python3 ./build-scripts/k8s_releases.py get_obsolete_prereleases`; do
+            branch="autoupdate/${outstandingPreRelease}"
+            if git branch -r | grep "origin/$branch"; then
+              echo "Cleaning up obsolete pre-release branch: $branch"
+              git push origin --delete $branch
+            else
+              echo "Obsolete branch not found, skpping: $branch"
+            fi
+          done

build-scripts/k8s_releases.py

@@ -28,9 +28,9 @@ def get_k8s_tags() -> List[str]:
 
 
 # k8s release naming:
-# * alpha:  v{major}.{minor}.{patch}r-alpha.{version}
-# * beta:   v{major}.{minor}.{patch}r-beta.{version}
-# * rc:     v{major}.{minor}.{patch}r-rc.{version}
+# * alpha:  v{major}.{minor}.{patch}-alpha.{version}
+# * beta:   v{major}.{minor}.{patch}-beta.{version}
+# * rc:     v{major}.{minor}.{patch}-rc.{version}
 # * stable: v{major}.{minor}.{patch}
 def is_stable_release(release: str):
     return "-" not in release
@@ -50,6 +50,14 @@ def get_latest_release() -> str:
     return k8s_tags[0]
 
 
+def get_outstanding_prerelease() -> str:
+    latest_release = get_latest_release()
+    if not is_stable_release(latest_release):
+        return latest_release
+    # The latest release is a stable release, no outstanding pre-release.
+    return None
+
+
 def get_obsolete_prereleases() -> List[str]:
     """Return obsolete K8s pre-releases.
 
@@ -75,4 +83,4 @@ def get_obsolete_prereleases() -> List[str]:
         for item in out:
             print(item)
     else:
-        print(out)
+        print(out or "")