sademban's blog

Blog Journal Portfolio About Now Uses Links 

Journal entries, build notes, and experiments from whatever I'm tinkering with next.

View on GitHub
6 October 2025

Slimming down the Docker images (multi-stage build)

by sademban

Abstract diagram showing build artifacts moving into a runtime container
Abstract builder-to-runtime flow for multi-stage Docker images

🐳 What does it mean to slim down a Docker image ?

Slimming down a Docker image means cutting away anything that does not need to ship with your application runtime. That typically includes trimming unused packages, choosing a smaller base image, flattening layers, and compiling only the binaries you actually ship. The goal is to leave behind the bare minimum that the container needs when it starts.

A slimmer image leaves less surface area for bugs and security issues, but the process often requires rethinking how your build stages work, what files are generated along the way, and how configuration is injected at runtime.

Multi-stage builds in practice

Multi-stage builds let you separate the heavy build toolchain from the lean runtime image. The first stage installs compilers, SDKs, and package managers so you can compile assets or binaries. A later stage starts from an ultra-minimal base image and COPY commands only the build outputs and essential configuration across. That pattern keeps your production image tiny while still giving you a full-featured environment during compilation and testing.

Common tactics include:

Advantages

Disadvantages

Known problems while slimming down

Bringing it together

Treat slimming as an iterative exercise: profile what your application needs, experiment with multi-stage builds, and automate validation so you catch missing dependencies early. Keep a heavier “debug” tag handy for operational use, and document the rationale for every tool you remove. That balance delivers lean images without sacrificing maintainability.

tags: docker - multi-stage - performance