Refactor Dockerfile and GitHub Actions for multi-architecture support

- Updated Dockerfile to copy the 'flapi' binary from the build stage.
- Modified GitHub Actions workflow to implement a matrix strategy for building on both linux/amd64 and linux/arm64 platforms, enhancing multiarch support.

Author: Joachim Rosskopf

.github/workflows/build.yaml

@@ -122,6 +122,9 @@ jobs:
     runs-on: ubuntu-latest
     if: github.event_name == 'push'
 
+    strategy:
+      matrix:
+        platform: [linux/amd64, linux/arm64]
     steps:
     - uses: actions/checkout@v4
 
@@ -149,14 +152,11 @@ jobs:
       with:
         context: .
         file: Dockerfile
-        platforms: linux/amd64,linux/arm64
+        platforms: ${{ matrix.platform }}
         push: true
         tags: |
           ghcr.io/${{ env.REPO_OWNER }}/flapi:latest
           ghcr.io/${{ env.REPO_OWNER }}/flapi:${{ github.sha }}
         provenance: false
-        build-args: |
-          TARGETARCH=${{ matrix.arch }}
         build-contexts: |
-          linux/amd64=artifacts/flapi-linux-amd64
-          linux/arm64=artifacts/flapi-linux-arm64
+          build=./artifacts/flapi-linux-${{ endsWith(matrix.platform, 'amd64') && 'amd64' || 'arm64' }}

Dockerfile

@@ -8,7 +8,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app
-COPY flapi /app/flapi
+COPY --from=build flapi /app/flapi
 RUN chmod +x /app/flapi
 
 ENTRYPOINT ["/app/flapi"]