Scenario

A microservice’s Docker image has grown to 1.5GB, slowing down deployments and consuming excessive storage. The Dockerfile installs dependencies, builds the Go application, and runs it.

Question

Describe how you would refactor this Dockerfile to significantly reduce the image size and improve build times.

Expected Answer

1. Multi-Stage Builds: Use a build stage (with full SDK) to compile the binary, and a runtime stage (distroless or alpine) for the final image.
2. Layer Caching: Order instructions from least changed to most changed (COPY go.mod -> go mod download -> COPY source -> go build).
3. Minimal Base Image: Use gcr.io/distroless/static or alpine for the final stage.
4. Impact: Expect size reduction to <50MB and faster sequential builds due to better caching.