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Docker & DevOps Fundamentals · Lesson

Multi-Stage Builds & Smaller Images

Learn how multi-stage Dockerfiles let you ship lean production images by separating build tools from the final runtime, dramatically reducing image size.

Multi-Stage Builds & Smaller Images 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

Large images are slow to build, push, and pull, and they carry a bigger attack surface. A good engineering goal is to ship the smallest image that still runs your app.

The Bloat Problem

Building an app often needs compilers, dev dependencies, and build tools. If those end up in the final image, it balloons in size — even though the running app does not need any of them.

What is a Multi-Stage Build?

A multi-stage build uses several FROM statements in one Dockerfile. Early stages build the app; the final stage copies only the finished artifacts, leaving build tools behind.

Naming a Stage

Give a stage a name with AS so later stages can refer to it.

FROM node:20 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci

Building in the First Stage

The build stage compiles or bundles your app. Here all dev dependencies and tooling are available.

COPY . .
RUN npm run build

A Lean Final Stage

Start the final stage from a minimal base image, then copy only what the app needs to run using COPY --from.

FROM node:20-slim
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules

Full Multi-Stage Dockerfile

Combining the stages produces a small final image that contains the built app but none of the build toolchain.

FROM node:20 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

FROM node:20-slim
WORKDIR /app
COPY --from=builder /app/dist ./dist
CMD ['node', 'dist/main.js']

Choosing a Small Base Image

The base image is often the biggest factor. Slim and Alpine variants shrink images significantly:

  • node:20 ~ large
  • node:20-slim ~ much smaller
  • node:20-alpine ~ smallest, minimal libs

Production-Only Dependencies

Skip dev dependencies in the runtime image. Installing with the production flag keeps test and build packages out.

RUN npm ci --omit=dev

Using .dockerignore

A .dockerignore file keeps junk out of the build context, speeding builds and avoiding accidental copies of secrets or huge folders.

node_modules
.git
.env
Dockerfile
*.log

Measuring the Result

Verify your work by checking image sizes. A well-built multi-stage image can be a fraction of a naive single-stage one.

docker images myapp

Quick Check

Test your multi-stage build knowledge.

Recap

You learned to ship lean Docker images:

  • Multi-stage builds use multiple FROM stages in one Dockerfile
  • Build in an early stage, then COPY --from only artifacts into a slim final stage
  • Pick small base images (slim/alpine) and install production-only deps
  • Use .dockerignore to trim the build context

Smaller images build faster, deploy quicker, and are more secure.

Frequently asked questions

Is the “Multi-Stage Builds & Smaller Images” lesson free?

Yes — the full text of “Multi-Stage Builds & Smaller Images” 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 “Multi-Stage Builds & Smaller Images”?

Learn how multi-stage Dockerfiles let you ship lean production images by separating build tools from the final runtime, dramatically reducing image size. 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 “Multi-Stage Builds & Smaller Images” 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

  1. Understanding Dockerfiles
  2. Creating Custom Docker Images
  3. Image Layers and Optimization
  4. Multi-Stage Builds & Smaller Images
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