Multi-Stage Builds
Refactor a bloated single-stage Dockerfile into a multi-stage build with named stages, separating compile-time tooling from a minimal runtime image.
Prerequisites: Completion of Dockerfile Fundamentals; a compiled-language sample app (this project uses Go) or any app with a distinct build step.
Targeted versions: Docker Engine 29.x with BuildKit (default builder); golang:1.25 build image; verified against docs.docker.com, mid-2026.
It's tempting to write a single-stage Dockerfile that installs a full compiler toolchain, builds your app, and ships that same image to production. The problem is that the compiler, build caches, and dev headers all ship with it — none of which your app needs at runtime, and all of which are attack surface and dead weight.
Multi-stage builds solve this by letting a single Dockerfile contain more than one FROM instruction. Each FROM starts a new, isolated build stage, and you selectively copy only the finished artifacts from one stage into the next, leaving the toolchain behind.
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