Start on building monolith image

Right now still the "old way," awaiting community input re: Dockerfiles

.github/workflows/cross-compiling-docker.yml

@@ -20,3 +20,35 @@ jobs:
       run: echo "CC=$(./.github/workflows/get-compiler.sh ccomp)" >> $GITHUB_ENV # https://stackoverflow.com/a/57969570/3551604
     - run: go env
     - run: ./build.sh
+    - name: upload build artifacts
+      uses: actions/upload-artifact@v2
+      with:
+        name: bin-${{ matrix.target }}
+        path: ./bin
+  build-monolith:
+    strategy:
+      matrix:
+        target: [amd64, arm64, arm]
+    env:
+      DOCKER_HUB_USER: dendritegithub
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/download-artifact@v2
+      with:
+        name: bin-${{ matrix.target }}
+    # - run: echo "RELEASE_VERSION=${GITHUB_REF#refs/*/}" >> $GITHUB_ENV
+    - run: echo "DOCKER_TARGET=$(./.github/workflows/get-compiler.sh docker)" >> $GITHUB_ENV 
+    # For building docker images, QEMU and buildx is still easier than anything to do with docker manifest editing
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v1
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v1
+    - name: Build image
+      uses: docker/build-push-action@v2
+      with:
+        context: .
+        file: ./build/docker/Dockerfile.monolith
+        platforms: ${{ env.PLATFORMS }}
+        push: false
+        tags: |
+          ${{ env.DOCKER_NAMESPACE }}/dendrite-monolith:latest

.github/workflows/get-compiler.sh

@@ -1,6 +1,24 @@
 #!/bin/bash
 set -eu
 
+# Given a GOARCH target, return what Docker calls that target.
+function get_docker() {
+    case "$GOARCH" in
+    "amd64")
+        echo "linux/amd64"
+        ;;
+    "arm64")
+        echo "linux/arm64/v8"
+        ;;
+    "arm")
+        echo "linux/arm/v7"
+        ;;
+    *)
+        exit 1
+        ;;
+    esac
+}
+
 # Given a GOARCH target, return the GCC for that target.
 function get_compiler() {
     case "$GOARCH" in
@@ -41,6 +59,9 @@ case "$1" in
 "ccomp")
     get_compiler
     ;;
+"docker")
+    get_docker
+    ;;
 *)
     exit 1
     ;;