Add a GitHub Actions workflow to build the Docker container image

.github/workflows/build-docker.yml

@@ -0,0 +1,143 @@
+name: Build Docker container image
+
+on:
+  push:
+    branches:
+      - 'main'
+      - 'beta'
+      - 'stable'
+    tags:
+      - 'v*'
+  pull_request:
+  merge_group:
+  workflow_dispatch:
+    inputs:
+      git-ref:
+        description: 'Git ref (optional)'
+        required: false
+
+env:
+  REGISTRY_IMAGE: ghcr.io/planktoscope/streamlit-classification-app
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        platform:
+          - linux/amd64
+          - linux/arm64
+          - linux/arm/v7
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Prepare environment variables
+        run: |
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV
+
+      # Build and publish Docker container image
+      - name: Get Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY_IMAGE }}
+          tags: |
+            type=sha
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push by digest
+        id: build
+        uses: docker/build-push-action@v5
+        with:
+          context: ./
+          pull: true
+          push: ${{ (github.event_name == 'pull_request' && !github.event.pull_request.head.repo.fork) || github.event_name == 'push' || github.event_name == 'push tag' }}
+          platforms: ${{ matrix.platform }}
+          tags: ${{ env.REGISTRY_IMAGE }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha,scope=build-${{ matrix.platform }}
+          cache-to: type=gha,mode=max,scope=build-${{ matrix.platform }}
+          outputs: type=image,name=${{ env.REGISTRY_IMAGE }},push-by-digest=true,name-canonical=true,push=${{ !github.event.pull_request.head.repo.fork }}
+
+      - name: Export digest
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ env.PLATFORM_PAIR }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge:
+    runs-on: ubuntu-latest
+    needs:
+      - build
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      # Build and publish Docker container image
+      - name: Get Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY_IMAGE }}
+          tags: |
+            type=match,pattern=v(.*),group=1
+            type=edge,branch=main
+            type=ref,event=branch,enable=${{ github.ref != format('refs/heads/{0}', 'main') && github.ref != format('refs/heads/{0}', 'main') }}
+            type=ref,event=pr
+            type=raw,value=latest,enable=${{ github.ref == format('refs/heads/{0}', 'stable') }}
+            type=sha
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GitHub Container Registry
+        uses: docker/login-action@v3
+        if: ${{ (github.event_name == 'pull_request' && !github.event.pull_request.head.repo.fork) || github.event_name == 'push' || github.event_name == 'push tag' }}
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Create manifest list and push
+        working-directory: /tmp/digests
+        if: ${{ (github.event_name == 'pull_request' && !github.event.pull_request.head.repo.fork) || github.event_name == 'push' || github.event_name == 'push tag' }}
+        run: |
+          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf '${{ env.REGISTRY_IMAGE }}@sha256:%s ' *)
+
+      - name: Inspect image
+        if: ${{ (github.event_name == 'pull_request' && !github.event.pull_request.head.repo.fork) || github.event_name == 'push' || github.event_name == 'push tag' }}
+        run: |
+          docker buildx imagetools inspect ${{ env.REGISTRY_IMAGE }}:${{ steps.meta.outputs.version }}