Build docker image in CI (#124)

.github/workflows/docker.yml

@@ -0,0 +1,52 @@
+name: SpacetimeDB Docker image
+
+on: "push"
+
+jobs:
+  docker:
+    runs-on: spacetimedb-runner
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v4
+        with:
+          images: |
+            clockworklabs/spacetimedb
+          tags: |
+            type=ref,event=branch,prefix=branch-
+            type=sha,prefix=commit-
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Cache Docker layers
+        uses: actions/cache@v2
+        with:
+          path: /tmp/.buildx-cache
+          key: ${{ runner.os }}-buildx-${{ github.sha }}
+          restore-keys: |
+            ${{ runner.os }}-buildx-
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ vars.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: crates/standalone/Dockerfile
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: |
+            ${{ steps.meta.outputs.tags }}
+          cache-from: type=local,src=/tmp/.buildx-cache
+          cache-to: type=local,dest=/tmp/.buildx-cache-new
+        # This ugly bit is necessary if you don't want your cache to grow forever
+        # until it hits GitHub's limit of 5GB.
+        # Temp fix
+        # https://github.com/docker/build-push-action/issues/252
+        # https://github.com/moby/buildkit/issues/1896
+      - name: Move cache
+        run: |
+          rm -rf /tmp/.buildx-cache
+          mv /tmp/.buildx-cache-new /tmp/.buildx-cache