ci: publish linux/arm64 Docker images

.github/workflows/ci.yml

@@ -29,4 +29,5 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - run: docker build .
+      - uses: docker/setup-buildx-action@v3
+      - run: docker buildx build --platform linux/amd64,linux/arm64 .

.github/workflows/docker-publish.yml

@@ -59,7 +59,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: .
-          platforms: linux/amd64
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}

Dockerfile

@@ -1,7 +1,11 @@
-# Build both the proxy and the test mock as static binaries.
-FROM golang:1.26 AS build
+# Build both the proxy and the test mock as static binaries. The build stage
+# runs natively on the builder and cross-compiles for the target platform, so
+# multi-arch builds need no emulation.
+FROM --platform=$BUILDPLATFORM golang:1.26 AS build
 WORKDIR /src
 COPY . .
+ARG TARGETOS
+ARG TARGETARCH
 ARG VERSION
 ARG COMMIT
 ARG BUILD_DATE
@@ -25,8 +29,9 @@ RUN set -eu; \
     d="${BUILD_DATE:-$(date -u +%Y-%m-%dT%H:%M:%SZ)}"; \
     dirty_flag="${DIRTY:-unknown}"; \
     ldflags="-s -w -X main.version=$v -X main.commit=$c -X main.buildDate=$d -X main.dirty=$dirty_flag"; \
-    CGO_ENABLED=0 go build -trimpath -buildvcs=false -ldflags "$ldflags" -o /out/steady-proxy .; \
-    CGO_ENABLED=0 go build -trimpath -buildvcs=false -o /out/testupstream ./testupstream
+    export CGO_ENABLED=0 GOOS="$TARGETOS" GOARCH="$TARGETARCH"; \
+    go build -trimpath -buildvcs=false -ldflags "$ldflags" -o /out/steady-proxy .; \
+    go build -trimpath -buildvcs=false -o /out/testupstream ./testupstream
 
 # Minimal runtime; distroless/static ships CA certs (needed for upstream TLS).
 FROM gcr.io/distroless/static-debian12

README.md

@@ -56,7 +56,7 @@ curl -fsS http://127.0.0.1:8789/__version
 
 ### Prebuilt container image
 
-Linux `amd64` images are published to GitHub Container Registry:
+Linux `amd64` and `arm64` images are published to GitHub Container Registry:
 
 ```bash
 docker pull ghcr.io/xllent-ai/steady-proxy:latest

docs/RELEASING.md

@@ -46,7 +46,7 @@ All steps use GitHub's built-in `GITHUB_TOKEN`; no external secrets are required
 
 ## Container images
 
-The [container workflow](../.github/workflows/docker-publish.yml) publishes Linux `amd64` images to `ghcr.io/xllent-ai/steady-proxy`:
+The [container workflow](../.github/workflows/docker-publish.yml) publishes multi-arch Linux `amd64` and `arm64` images to `ghcr.io/xllent-ai/steady-proxy`:
 
 - **Push to `main`:** Publishes `latest` and `sha-<full-commit-sha>`.
 - **Release published:** Publishes `<release-tag>` (e.g., `v0.1.1`) and `sha-<full-commit-sha>`. Release builds never overwrite `latest`.