fix multi-platform build (#6)

.github/workflows/call-docker-build-promote.yaml

@@ -33,14 +33,15 @@ jobs:
  dockerhub-enable: false
  ghcr-enable: true
  push: true
+ platforms: linux/amd64,linux/arm64
  image-names: |
  ghcr.io/${{ github.repository }}
 
  scan-pr:
  name: CVE Scan
  if: github.event_name == 'pull_request'
  needs: docker-build-pr
- permissions: 
+ permissions:
  packages: read
  uses: mostlydevops/actions/.github/workflows/reusable-trivy-scan-image.yaml@main
  secrets:
@@ -61,10 +62,11 @@ jobs:
  packages: write
  pull-requests: write
  uses: mostlydevops/actions/.github/workflows/reusable-docker-build.yaml@main
- with: 
+ with:
  dockerhub-enable: false
  ghcr-enable: true
  push: true
+ platforms: linux/amd64,linux/arm64
  image-names: |
  ghcr.io/${{ github.repository }}
  ghcr.io/${{ github.repository }}-stable

Dockerfile

@@ -1,14 +1,23 @@
 # BUILD
-FROM golang:alpine as builder
+# use the build platforms matching arch rather than target arch
+FROM --platform=$BUILDPLATFORM golang:alpine as builder
+
+ARG TARGETARCH
+
+WORKDIR /go
 
 COPY dispatcher.go .
-RUN go build dispatcher.go
+
+# build for the target arch not the build platform host arch
+RUN GOOS=linux GOARCH=$TARGETARCH go build dispatcher.go
 
 # RUN
-FROM alpine
+# defaults to using the target arch image
+FROM scratch as run
+
+COPY --from=builder /go/dispatcher /dispatcher
+COPY static /static/
 
 EXPOSE 80
-CMD ["/dispatcher"]
 
-COPY --from=builder /go/dispatcher /
-COPY static /static/
+CMD ["/dispatcher"]