Add Docker build CI

Author: Menci

.github/workflows/build.yaml

@@ -0,0 +1,49 @@
+name: Build and Push
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - name: with rootfs
+            image-name: menci/syzoj-judge
+            dockerfile: Dockerfile
+          - name: without rootfs
+            image-name: menci/syzoj-judge-norootfs
+            dockerfile: Dockerfile.NOROOTFS
+    name: Build and Push (${{ matrix.target.name }})
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up QEMU
+        uses: docker/setup-buildx-action@v1
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Generate Tag List
+        run: |
+          echo "TAGS<<EOF" >> $GITHUB_ENV
+
+          HASH_SHORT="$(git rev-parse --short HEAD)"
+          echo $IMAGE_NAME:$HASH_SHORT >> $GITHUB_ENV
+          echo $IMAGE_NAME:latest >> $GITHUB_ENV
+
+          echo "EOF" >> $GITHUB_ENV
+        env:
+          IMAGE_NAME: ${{ matrix.target.image-name }}
+      - name: Build and Push
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/amd64
+          push: true
+          tags: ${{ env.TAGS }}
+          file: ${{ matrix.target.dockerfile }}