ops: Add a Docker image builder workflow

.github/workflows/on-tag.yml

@@ -0,0 +1,97 @@
+name: Docker build on tag
+env:
+  DOCKER_CLI_EXPERIMENTAL: enabled
+  TAG_FMT: "^refs/tags/(((.?[0-9]+){3,4}))$"
+  DOCKER_BUILDKIT: 0
+  COMPOSE_DOCKER_CLI_BUILD: 0
+
+on:
+  push:
+    tags:
+      - v[0-9]+.[0-9]+.[0-9]+
+      - v[0-9]+.[0-9]+.[0-9]+-*
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    timeout-minutes: 120
+    name: Build and push to DockerHub
+    steps:
+      # Workaround based on JonasAlfredsson/[email protected]
+      - name: Replace the current swap file
+        shell: bash
+        run: |
+          sudo swapoff /mnt/swapfile
+          sudo rm -v /mnt/swapfile
+          sudo fallocate -l 13G /mnt/swapfile
+          sudo chmod 600 /mnt/swapfile
+          sudo mkswap /mnt/swapfile
+          sudo swapon /mnt/swapfile
+
+      - name: Show current memory and swap status
+        shell: bash
+        run: |
+          sudo free -h
+          echo
+          sudo swapon --show
+
+      - name: Mount a tmpfs over /var/lib/docker
+        shell: bash
+        run: |
+          if [ ! -d "/var/lib/docker" ]; then
+            echo "Directory '/var/lib/docker' not found"
+            exit 1
+          fi
+          sudo mount -t tmpfs -o size=10G tmpfs /var/lib/docker
+          sudo systemctl restart docker
+          sudo df -h | grep docker
+
+      - name: Set env variables
+        run: echo "TAG=${GITHUB_REF/refs\/tags\//}" >> $GITHUB_ENV
+
+      - name: Show set environment variables
+        run: |
+          printf "      TAG: %s\n"  "$TAG"
+
+      - name: Add SHORT_SHA env property with commit short sha
+        run: echo "SHORT_SHA=`echo ${GITHUB_SHA} | cut -c1-8`" >> $GITHUB_ENV
+
+      - name: Login to Docker for building
+        run: echo "${{ secrets.DOCKER_PASSWORD }}" | docker login -u "${{ secrets.DOCKER_USERNAME }}" --password-stdin
+
+      - name: Checkout project
+        uses: actions/checkout@v3
+
+      # - name: Set up QEMU
+      #   uses: docker/setup-qemu-action@v3
+      #   id: qemu
+
+      - name: Setup Docker buildx action
+        uses: docker/setup-buildx-action@v3
+        id: buildx
+
+      - name: Available platforms
+        run: echo ${{ steps.buildx.outputs.platforms }}
+
+      - name: Cache Docker layers
+        uses: actions/cache@v3
+        id: cache
+        with:
+          path: /tmp/.buildx-cache
+          key: ${{ runner.os }}-buildx
+          restore-keys: |
+            ${{ runner.os }}-buildx
+
+      - name: Run Docker buildx against tag
+        run: |
+          docker buildx build \
+          --cache-from "type=local,src=/tmp/.buildx-cache" \
+          --cache-to "type=local,dest=/tmp/.buildx-cache" \
+          --platform linux/amd64 \
+          --tag ${{ secrets.DOCKER_USERNAME }}/electrs:$TAG \
+          --tag ${{ secrets.DOCKER_USERNAME }}/electrs:latest \
+          --output "type=registry" . \
+          --build-arg commitHash=$SHORT_SHA