fix(ci): speed up docker build

trying two things:
- speed up arm build by allowing cross-comp from go instead of slow QEMU
- take a stab at caching buildx layers, without infinite growth

This fix was laready applied in
ipfs-inactive/bifrost-gateway@14cfa48
and reduced build time from 20m to 3m.

.github/workflows/docker-image.yml

@@ -31,6 +31,14 @@ jobs:
       - 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: |
+            ${{ runner.os }}-buildx-
+
       - name: Get tags
         id: tags
         run: |
@@ -53,3 +61,12 @@ jobs:
           push: true
           file: ./Dockerfile
           tags: "${{ steps.tags.outputs.value }}"
+          cache-from: type=local,src=/tmp/.buildx-cache
+          cache-to: type=local,dest=/tmp/.buildx-cache-new
+
+      # https://github.com/docker/build-push-action/issues/252
+      # https://github.com/moby/buildkit/issues/1896
+      - name: Move cache to limit growth
+        run: |
+          rm -rf /tmp/.buildx-cache
+          mv /tmp/.buildx-cache-new /tmp/.buildx-cache

Dockerfile

@@ -1,6 +1,11 @@
-FROM golang:1.19.1-buster
+FROM --platform=${BUILDPLATFORM:-linux/amd64} golang:1.19.1-buster
 LABEL maintainer="Steven Allen <steven@stebalien.com>"
 
+ARG TARGETPLATFORM
+ARG BUILDPLATFORM
+ARG TARGETOS
+ARG TARGETARCH
+
 # Install deps
 RUN apt-get update && apt-get install -y \
   libssl-dev \
@@ -24,7 +29,7 @@ ARG IPFS_PLUGINS
 # Also: fix getting HEAD commit hash via git rev-parse.
 RUN cd $SRC_DIR \
   && mkdir -p .git/objects \
-  && GOFLAGS=-buildvcs=false make build GOTAGS=openssl IPFS_PLUGINS=$IPFS_PLUGINS
+  && GOOS=$TARGETOS GOARCH=$TARGETARCH GOFLAGS=-buildvcs=false make build GOTAGS=openssl IPFS_PLUGINS=$IPFS_PLUGINS
 
 # Get su-exec, a very minimal tool for dropping privileges,
 # and tini, a very minimal init daemon for containers
@@ -46,7 +51,7 @@ RUN set -eux; \
   && chmod +x tini
 
 # Now comes the actual target image, which aims to be as small as possible.
-FROM busybox:1.31.1-glibc
+FROM --platform=${BUILDPLATFORM:-linux/amd64} busybox:1.31.1-glibc
 LABEL maintainer="Steven Allen <steven@stebalien.com>"
 
 # Get the ipfs binary, entrypoint script, and TLS CAs from the build container.