Minimizing Image Size with Slim and Distroless Bases
Shrink final images by choosing minimal base images, removing build tooling, and using distroless or scratch bases for faster pulls and a smaller attack surface.
Minimizing Image Size with Slim and Distroless Bases is a free Docker & DevOps Fundamentals lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Docker & DevOps Fundamentals learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why Image Size Matters
Smaller images pull faster, start quicker, cost less to store, and expose fewer packages to attackers. Optimizing size is both a performance and a security win.
Choosing a Lean Base
Default images are convenient but heavy. Swapping node:20 (~1GB) for node:20-slim or node:20-alpine can cut hundreds of megabytes instantly.
FROM node:20-slimAlpine Trade-offs
Alpine is tiny but uses musl libc instead of glibc, which occasionally breaks native binaries. Test carefully; sometimes -slim is the safer small option.
FROM python:3.12-alpineCombine RUN Layers
Each RUN adds a layer. Chain related commands and clean up in the same layer, or the deleted files still bloat the earlier layer.
RUN apt-get update \
&& apt-get install -y curl \
&& rm -rf /var/lib/apt/lists/*Use .dockerignore
A .dockerignore file keeps junk out of the build context: node_modules, .git, logs. Less context means faster builds and smaller layers.
# .dockerignore
.git
node_modules
*.logMulti-Stage Recap
Build in one stage with all the compilers, then COPY --from only the artifact into a clean final stage. The toolchain never ships.
FROM golang:1.22 AS build
WORKDIR /src
COPY . .
RUN go build -o app
FROM alpine:3.20
COPY --from=build /src/app /appMeet Distroless
Distroless images contain only your app and its runtime - no shell, no package manager, no extra binaries. Tiny and hard to exploit.
FROM gcr.io/distroless/static-debian12
COPY --from=build /src/app /app
ENTRYPOINT ["/app"]No Shell, No Problem
Distroless has no shell, so RUN commands and docker exec sh will not work. Do all setup in earlier stages; use the :debug tag when you must poke inside.
The scratch Base
For fully static binaries (Go, Rust), FROM scratch ships nothing but your executable - often a few megabytes total.
FROM scratch
COPY --from=build /src/app /app
ENTRYPOINT ["/app"]Measuring Your Wins
Use docker images to compare sizes and docker history to see which layers are biggest. Optimize the fattest layers first.
docker history myapp:latestPin Versions, Not latest
Pinning a specific tag or digest makes builds reproducible and avoids surprise size jumps when an upstream latest changes.
FROM node:20.11.1-slimQuick Check
What is special about a distroless image?
Recap
You can now shrink images aggressively:
- Pick
-slim,-alpine, distroless, orscratchbases - Chain and clean
RUNlayers; use.dockerignore - Multi-stage builds drop the toolchain
- Measure with
docker historyand pin versions
Smaller images mean faster, safer deployments.
Frequently asked questions
Is the “Minimizing Image Size with Slim and Distroless Bases” lesson free?
Yes — the full text of “Minimizing Image Size with Slim and Distroless Bases” is free to read here on the web, and the Docker & DevOps Fundamentals course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Docker & DevOps Fundamentals course, upgrade to CoddyKit PRO.
What will I learn in “Minimizing Image Size with Slim and Distroless Bases”?
Shrink final images by choosing minimal base images, removing build tooling, and using distroless or scratch bases for faster pulls and a smaller attack surface. You practise Docker & DevOps Fundamentals with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Docker & DevOps Fundamentals?
No prior experience is required. Docker & DevOps Fundamentals on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Minimizing Image Size with Slim and Distroless Bases” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Docker & DevOps Fundamentals lesson?
Yes. Every Docker & DevOps Fundamentals lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Multi-Stage Builds for Efficiency
- Leveraging Build Caching
- Dockerfile Security Best Practices
- Minimizing Image Size with Slim and Distroless Bases