ci: publish Docker images to GHCR alongside Docker Hub (#7569)

* ci: publish Docker images to GHCR alongside Docker Hub

Adds ghcr.io/ether/etherpad as a second publish target on release tags,
reusing the existing docker/metadata-action step so the same SemVer tags
(e.g. 2.6.1, 2.6, 2, latest) are pushed to both registries.

Motivation: downstream consumers (Helm charts in particular) hit Docker
Hub anonymous pull rate limits. GHCR has no such limits and the
workflow already runs with GITHUB_TOKEN, so this is additive with no
new secrets required.

Docker Hub remains the primary/canonical source; GHCR is a mirror.

Note: this only affects future release tags. The 2.6.1 tag already on
Docker Hub will need to be mirrored separately (e.g. via skopeo) if
downstream needs it on GHCR before the next release.

* address qodo review: scope packages:write to publish job, document GHCR

Two fixes from the qodo code review on #7569:

1. Overprivileged PR token (security). The original change set
   'packages: write' at workflow level, which meant pull_request runs
   (whose Test step executes PR-controlled code) also inherited push
   access to GHCR. Splits the workflow into two jobs:
     - build-test: runs on pull_request and push with contents:read
       only. Does the single-arch load+test as before.
     - publish: needs build-test, runs only on push with
       packages:write. Does the multi-arch build-and-push, Docker Hub
       description update, and ether-charts bump.
   Docker Hub login is also now gated by job-level 'if' (same effect
   as the previous step-level 'if').

2. Docs miss GHCR option. Updates doc/docker.md and README.md to
   document the GHCR mirror alongside Docker Hub with equivalent pull
   examples, so downstream users discovering via docs can choose the
   mirror to avoid Docker Hub rate limits.

.github/workflows/docker.yml

@@ -12,12 +12,15 @@ on:
       - 'v?[0-9]+.[0-9]+.[0-9]+'
 env:
   TEST_TAG: etherpad/etherpad:test
+
 permissions:
   contents: read
 
 jobs:
-  docker:
+  build-test:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     env:
       PNPM_HOME: ~/.pnpm-store
     steps:
@@ -26,11 +29,6 @@ jobs:
         uses: actions/checkout@v6
         with:
           path: etherpad
-
-      -
-        name: Set up QEMU
-        if: github.event_name == 'push'
-        uses: docker/setup-qemu-action@v4
       -
         name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v4
@@ -78,13 +76,34 @@ jobs:
           done
           (cd src && gnpm run test-container)
           git clean -dxf .
+
+  publish:
+    needs: build-test
+    if: github.event_name == 'push'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      -
+        name: Check out
+        uses: actions/checkout@v6
+        with:
+          path: etherpad
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v4
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v4
       -
         name: Docker meta
-        if: github.event_name == 'push'
         id: meta
         uses: docker/metadata-action@v6
         with:
-          images: etherpad/etherpad
+          images: |
+            etherpad/etherpad
+            ghcr.io/ether/etherpad
           tags: |
             type=ref,event=branch
             type=semver,pattern={{version}}
@@ -92,15 +111,20 @@ jobs:
             type=semver,pattern={{major}}
       -
         name: Log in to Docker Hub
-        if: github.event_name == 'push'
         uses: docker/login-action@v4
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Log in to GHCR
+        uses: docker/login-action@v4
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
       -
         name: Build and push
         id: build-docker
-        if: github.event_name == 'push'
         uses: docker/build-push-action@v7
         with:
           context: ./etherpad
@@ -109,6 +133,7 @@ jobs:
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
       - name: Update repo description
         uses: peter-evans/dockerhub-description@v5
         if: github.ref == 'refs/heads/master'
@@ -118,8 +143,8 @@ jobs:
           password: ${{ secrets.DOCKERHUB_TOKEN }}
           repository: etherpad/etherpad
           enable-url-completion: true
-      - name: Check out
-        if: github.event_name == 'push' && github.ref == 'refs/heads/develop'
+      - name: Check out ether-charts
+        if: github.ref == 'refs/heads/develop'
         uses: actions/checkout@v6
         with:
           path: ether-charts

README.md

@@ -103,11 +103,13 @@ $env:ETHERPAD_RUN=1; irm https://raw.githubusercontent.com/ether/etherpad/master
 
 ### Docker-Compose
 
+The official image is published to both Docker Hub (`etherpad/etherpad`) and GitHub Container Registry (`ghcr.io/ether/etherpad`) with identical tags. Use whichever suits your environment; GHCR avoids Docker Hub's anonymous pull rate limits.
+
 ```yaml
 services:
   app:
     user: "0:0"
-    image: etherpad/etherpad:latest
+    image: etherpad/etherpad:latest  # or: ghcr.io/ether/etherpad:latest
     tty: true
     stdin_open: true
     volumes:

doc/docker.md

@@ -1,15 +1,21 @@
 # Docker
 
-The official Docker image is available on https://hub.docker.com/r/etherpad/etherpad.
+The official Docker image is published to two registries with identical tags:
 
-## Downloading from Docker Hub
-If you are ok downloading a [prebuilt image from Docker Hub](https://hub.docker.com/r/etherpad/etherpad), these are the commands:
+- Docker Hub (canonical): https://hub.docker.com/r/etherpad/etherpad
+- GitHub Container Registry (mirror): https://github.com/ether/etherpad/pkgs/container/etherpad
+
+The GHCR mirror is useful if you are hitting Docker Hub anonymous pull rate limits (for example on Kubernetes clusters).
+
+## Downloading a prebuilt image
 ```bash
-# gets the latest published version
+# from Docker Hub
 docker pull etherpad/etherpad
-
-# gets a specific version
 docker pull etherpad/etherpad:2.6.1
+
+# from GHCR (same image, same tags)
+docker pull ghcr.io/ether/etherpad
+docker pull ghcr.io/ether/etherpad:2.6.1
 ```
 
 ## Build a personalized container