ci(docker): build and publish the ui image for amd64 and arm64

.github/workflows/docker.yml

@@ -0,0 +1,79 @@
+name: Docker image
+
+# Builds visualregressiontracker/ui for linux/amd64 and linux/arm64 (Apple Silicon,
+# Graviton), so docker compose runs it natively instead of under emulation.
+# - pushing a vX.Y.Z tag publishes the image as X.Y.Z
+# - "Run workflow" with an existing tag (re)publishes it, e.g. to add arm64 to a released version
+# - pull requests that touch the image only build it, without pushing
+# Publishing needs the DOCKERHUB_USERNAME and DOCKERHUB_TOKEN repository secrets.
+
+on:
+  push:
+    tags:
+      - 'v*'
+  pull_request:
+    branches: [master]
+    paths:
+      - Dockerfile
+      - env.sh
+      - nginx/**
+      - .github/workflows/docker.yml
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: Existing tag to publish, e.g. v5.6.0
+        required: true
+
+# GITHUB_TOKEN is only used to check out the code; image pushes use the Docker Hub secrets
+permissions:
+  contents: read
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Resolve version
+        id: version
+        env:
+          TAG: ${{ inputs.tag || github.ref_name }}
+        run: |
+          if [ "$GITHUB_EVENT_NAME" = "pull_request" ]; then
+            echo "push=false" >> "$GITHUB_OUTPUT"
+          elif [ "${TAG#v}" != "$TAG" ]; then
+            echo "push=true" >> "$GITHUB_OUTPUT"
+            echo "version=${TAG#v}" >> "$GITHUB_OUTPUT"
+          else
+            echo "::error::Tag $TAG does not look like vX.Y.Z"
+            exit 1
+          fi
+
+      - uses: actions/checkout@v4
+        with:
+          # a manual run checks out the tag itself, never a branch with the same name
+          ref: ${{ inputs.tag && format('refs/tags/{0}', inputs.tag) || github.ref }}
+          # keep the token out of .git/config, which is part of the build context
+          persist-credentials: false
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@c7c53464625b32c7a7e944ae62b3e17d2b600130 # v3.7.0
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f # v3.12.0
+
+      - name: Log in to Docker Hub
+        if: steps.version.outputs.push == 'true'
+        uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3.7.0
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@10e90e3645eae34f1e60eeb005ba3a3d33f178e8 # v6.19.2
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: ${{ steps.version.outputs.push == 'true' }}
+          tags: visualregressiontracker/ui:${{ steps.version.outputs.version || 'ci' }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

Dockerfile

@@ -1,6 +1,7 @@
 ### STAGE 1: Build ###
 # This image is around 50 megabytes
-FROM node:20-alpine AS builder
+# The built ui is static files, so build it once on the native platform for every target platform
+FROM --platform=$BUILDPLATFORM node:20-alpine AS builder
 
 # Create app directory
 WORKDIR /app