feat: add multi-arch build (amd64 + arm64) (#21)

* feat: add multi-arch build (amd64 + arm64)

Add QEMU and platform support to build Docker images for both
linux/amd64 and linux/arm64 architectures.

* perf: use native Go cross-compilation instead of QEMU emulation

Author: awbait

.github/workflows/release.yaml

@@ -26,6 +26,9 @@ jobs:
           type=raw,value=latest,enable=${{ startsWith(github.ref, 'refs/tags/') }}
           type=sha
 
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v3
+
     - name: Set up Docker Buildx
       id: buildx
       uses: docker/setup-buildx-action@v3
@@ -41,6 +44,7 @@ jobs:
       uses: docker/build-push-action@v5
       with:
         context: .
+        platforms: linux/amd64,linux/arm64
         build-args: |
           versionflags=-X 'main.appVersion=${{ github.ref_name }}'
         push: ${{ github.event_name != 'pull_request' }}

Dockerfile

@@ -1,6 +1,7 @@
 # https://hub.docker.com/_/golang
-FROM docker.io/library/golang:1.25.3-alpine AS build
+FROM --platform=$BUILDPLATFORM docker.io/library/golang:1.25.3-alpine AS build
 
+ARG TARGETARCH
 ARG versionflags=""
 
 WORKDIR /src
@@ -9,7 +10,7 @@ COPY . .
 
 RUN go mod download
 
-RUN CGO_ENABLED=0 go build -o webhook -ldflags "-w -s -extldflags '-static' ${versionflags}" .
+RUN CGO_ENABLED=0 GOARCH=${TARGETARCH} go build -o webhook -ldflags "-w -s -extldflags '-static' ${versionflags}" .
 
 FROM gcr.io/distroless/static-debian12:nonroot AS webhook