Add fast Docker layer caching to CI

This is done using Docker's own released actions in combination with GitHub's caching actions.
A local package registry is used, and has been added to Dockerfile(s) as ARGs.
These ARGs do not interfere with local Docker builds in my testing.
Individual caches are used to speed up caching (see: docker/build-push-action#252 (comment))

.github/dependabot.yml

@@ -0,0 +1,7 @@
+version: 2
+updates:
+  # Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"

.github/workflows/dockerimage.yml

@@ -3,15 +3,68 @@ name: Docker Image CI
 on: [push]
 
 jobs:
-  build:
+  build_test_project:
     runs-on: ubuntu-latest
+    services:
+      registry:
+        image: registry:2
+        ports:
+          - 5000:5000
     steps:
     - uses: actions/checkout@v2
-    - name: Build colonists-shared
-      run: docker build --tag colonists/colonists-shared:$(git log --pretty=format:'%h' -n 1) --build-arg BRANCH_TAG=$(git log --pretty=format:'%h' -n 1) ./colonists-shared
-    - name: Build colonists-server
-      run: docker build --tag colonists/colonists-server:$(git log --pretty=format:'%h' -n 1) --build-arg BRANCH_TAG=$(git log --pretty=format:'%h' -n 1) ./colonists-server
-    - name: Build colonists-client
-      run: docker build --tag colonists/colonists-client:$(git log --pretty=format:'%h' -n 1) --build-arg BRANCH_TAG=$(git log --pretty=format:'%h' -n 1) ./colonists-client
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v1
+      with:
+          driver-opts: network=host
+    - name: Set colonists-shared cache
+      uses: actions/cache@v2
+      with:
+        path: /tmp/.buildx-cache-shared
+        key: ${{ runner.os }}-buildx-${{ github.sha }}
+        restore-keys: |
+          ${{ runner.os }}-buildx-
+    - name: Set colonists-server cache
+      uses: actions/cache@v2
+      with:
+        path: /tmp/.buildx-cache-server
+        key: ${{ runner.os }}-buildx-${{ github.sha }}
+        restore-keys: |
+          ${{ runner.os }}-buildx-
+    - name: Set colonists-client cache
+      uses: actions/cache@v2
+      with:
+        path: /tmp/.buildx-cache-client
+        key: ${{ runner.os }}-buildx-${{ github.sha }}
+        restore-keys: |
+          ${{ runner.os }}-buildx-
+    - name: Build shared
+      uses: docker/build-push-action@v2
+      with:
+        push: true
+        tags: localhost:5000/colonists/colonists-shared
+        cache-from: type=local,src=/tmp/.buildx-cache-shared
+        cache-to: type=local,dest=/tmp/.buildx-cache-shared
+        context: ./colonists-shared
     - name: Run shared tests
-      run: docker run --rm colonists/colonists-shared:$(git log --pretty=format:'%h' -n 1)
+      run: docker run --rm localhost:5000/colonists/colonists-shared
+    - name: Build server
+      uses: docker/build-push-action@v2
+      with:
+        push: false
+        tags: colonists/colonists-server
+        cache-from: type=local,src=/tmp/.buildx-cache-server
+        cache-to: type=local,dest=/tmp/.buildx-cache-server
+        context: ./colonists-server
+        build-args: |
+          "LOCAL_REGISTRY=localhost:5000/"
+    - name: Build client
+      uses: docker/build-push-action@v2
+      with:
+        push: false
+        tags: colonists/colonists-client
+        cache-from: type=local,src=/tmp/.buildx-cache-client
+        cache-to: type=local,dest=/tmp/.buildx-cache-client
+        context: ./colonists-client
+        build-args: |
+          "LOCAL_REGISTRY=localhost:5000/"
+        

colonists-client/Dockerfile

@@ -1,6 +1,7 @@
 # Library
 ARG BRANCH_TAG=latest
-FROM colonists/colonists-shared:${BRANCH_TAG} as library
+ARG LOCAL_REGISTRY=
+FROM ${LOCAL_REGISTRY}colonists/colonists-shared:${BRANCH_TAG} as library
 
 # Cache
 FROM node:alpine as dependency-cache-client

colonists-server/Dockerfile

@@ -1,5 +1,6 @@
 ARG BRANCH_TAG=latest
-FROM colonists/colonists-shared:${BRANCH_TAG} as library
+ARG LOCAL_REGISTRY
+FROM ${LOCAL_REGISTRY}colonists/colonists-shared:${BRANCH_TAG} as library
 
 FROM node as dependency-cache-server
 WORKDIR /cache