feat: add multiplatform docker image build (#18)

The build is very slow for some reason. ~15mins

.github/workflows/docker.yaml

@@ -33,13 +33,15 @@ jobs:
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}
             type=semver,pattern={{major}}
-            type=sha
       -
         name: Set up QEMU
         uses: docker/setup-qemu-action@v1
       -
         name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
+        with:
+          version: latest
+          buildkitd-flags: --debug
       -
         name: Login to ghcr.io
         uses: docker/login-action@v1 
@@ -61,6 +63,5 @@ jobs:
           context: .
           push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
+          platforms: linux/amd64,linux/arm64,linux/arm/v7
           labels: ${{ steps.meta.outputs.labels }}
-          cache-from: type=gha
-          cache-to: type=gha,mode=max

Dockerfile

@@ -1,11 +1,14 @@
 FROM golang:1.17-alpine AS build
 
+ENV CGO_ENABLED=0
 ENV PORT 10000
 
 COPY . /go/src/ondemand-service
 WORKDIR /go/src/ondemand-service
 
-RUN go build -o /go/bin/ondemand-service
+ARG TARGETOS
+ARG TARGETARCH
+RUN GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -o /go/bin/ondemand-service
 
 FROM alpine
 EXPOSE 10000