Use the Docker image as a source of cache layers

.github/workflows/dockerimage.yml

@@ -9,23 +9,44 @@ on:
 jobs:
 
   build:
-
     runs-on: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v2
 
     - name: Build the Docker image
+      env:
+        CACHE_IMAGE: macbre/nginx-brotli:latest
+
+        # @see https://docs.docker.com/develop/develop-images/build_enhancements/
+        COMPOSE_DOCKER_CLI_BUILD: "1"
+        DOCKER_BUILDKIT: "1"
+
       run: |
-        docker build . --tag ${{ github.repository }}
+        # build an image using the current Docker Hub container image as a layers cache
+
+        # @see https://docs.docker.com/engine/reference/commandline/build/#specifying-external-cache-sources
+        # no need to "docker pull $CACHE_IMAGE", BuildKit is clever enough to pull it when needed
+        docker build . \
+          --tag ${{ github.repository }} \
+           --build-arg BUILDKIT_INLINE_CACHE=1 \
+          --cache-from $CACHE_IMAGE
         docker images
 
     - name: Run nginx -V
       run: docker run -t ${{ github.repository }} nginx -V
 
     - name: Serve a static asset
       run: |
-        docker run --detach --rm -p 0.0.0.0:8888:80 -v "$PWD/tests":/static:ro  -v "$PWD/tests/static.conf":/etc/nginx/conf.d/static.conf:ro -v "$PWD/tests/env.conf":/etc/nginx/main.d/env.conf:ro --env FOO=foo-test-value --name test_nginx -t ${{ github.repository }}
+        docker run --detach --rm \
+          -p 0.0.0.0:8888:80 \
+          -v "$PWD/tests":/static:ro \
+          -v "$PWD/tests/static.conf":/etc/nginx/conf.d/static.conf:ro \
+          -v "$PWD/tests/env.conf":/etc/nginx/main.d/env.conf:ro \
+          --env FOO=foo-test-value \
+          --name test_nginx \
+          -t ${{ github.repository }}
+
         sleep 2; docker ps
         curl -v --compressed 0.0.0.0:8888 2>&1 | tee /tmp/out