Three Simple Tricks for Smaller Docker Images: Multi‑Stage Builds, Distroless, and Alpine

When building Docker containers, a smaller image speeds up transfer and deployment, but each RUN statement creates a new layer and intermediate files, increasing size.

Combining commands with && reduces layers, yet the most effective method is using multi‑stage builds, which allow you to copy only the final artifacts into a clean image.

Example: a simple Node.js app (index.js and package.json) is first built in a stage that installs dependencies, then copied into a second stage. The resulting image has far fewer layers and is considerably smaller.

FROM node:8 as build
WORKDIR /app
COPY package.json index.js ./
RUN npm install
FROM node:8
COPY --from=build /app /
EXPOSE 3000
CMD ["npm", "start"]

Running docker build -t node-multi-stage . and inspecting the history shows only three layers in the final image, compared to five layers in a single‑stage build.

Further size reduction can be achieved with distroless images, which contain only the application and its runtime dependencies, omitting package managers, shells, and other binaries. Switching the final stage to gcr.io/distroless/nodejs reduces the image to about 76 MB.

FROM node:8 as build
WORKDIR /app
COPY package.json index.js ./
RUN npm install
FROM gcr.io/distroless/nodejs
COPY --from=build /app /
EXPOSE 3000
CMD ["index.js"]

Alternatively, using an Alpine base image ( node:8-alpine ) yields an even smaller image (~70 MB) while still providing a shell for debugging. However, Alpine uses musl libc instead of glibc , which can cause compatibility issues with pre‑compiled binaries.

FROM node:8 as build
WORKDIR /app
COPY package.json index.js ./
RUN npm install
FROM node:8-alpine
COPY --from=build /app /
EXPOSE 3000
CMD ["npm", "start"]

Choosing the right base image depends on priorities: distroless offers the smallest footprint and better security (no shell), Alpine offers a tiny size with a shell but may have compatibility challenges, and the original Ubuntu‑based image is larger but provides a full development environment.

Size comparison:

node:8 – 681 MB

node:8 with multi‑stage – 678 MB

distroless nodejs – 76.7 MB

node:8‑alpine – 69.7 MB

In production, prioritize security with distroless; for debugging or when size is the only concern, Alpine may be preferable; the full Ubuntu image remains useful for testing and development.