Add multi-platform Docker build support

- Enable building for linux/amd64 and linux/arm64 platforms
- Use build-time platform variables in Dockerfile
- Optimize Go build with CGO disabled and trimmed binaries

Author: hrntknr

.github/workflows/docker-build.yaml

@@ -47,5 +47,6 @@ jobs:
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
+          platforms: linux/amd64,linux/arm64
           cache-from: type=gha
           cache-to: type=gha,mode=max

Dockerfile

@@ -1,10 +1,12 @@
-FROM docker.io/library/golang:alpine AS builder
+FROM --platform=$BUILDPLATFORM docker.io/library/golang:alpine AS builder
 
 WORKDIR /app
 COPY go.mod go.sum ./
 RUN go mod download
 COPY ./ /app
-RUN go build -o bin/main .
+
+ARG TARGETARCH
+RUN CGO_ENABLED=0 GOARCH=$TARGETARCH go build -trimpath -ldflags '-w -s' -o bin/main .
 
 FROM docker.io/library/alpine:latest