Create Multistage Dockerfile

Create Multi-Stage Dockerfile

Build multi-stage Dockerfiles that produce minimal production images by separating build tooling from runtime.

When to Use

• Production images are too large (>500MB for compiled languages)
• Build tools (compilers, dev headers) are included in the final image
• Need separate images for development and production from one Dockerfile
• Deploying to constrained environments (edge, serverless)

Inputs

• Required: Existing Dockerfile or project to containerize
• Required: Language and build system (npm, pip, go build, cargo, maven)
• Optional: Target runtime base (slim, alpine, distroless, scratch)
• Optional: Size budget for final image

Procedure

Step 1: Identify Build vs Runtime Dependencies

Step 2: Structure the Multi-Stage Build

The core pattern: build in a fat image, copy artifacts to a slim image.

# ---- Build Stage ----
FROM <build-image> AS builder
WORKDIR /src
COPY <dependency-manifest> .
RUN <install-dependencies>
COPY . .
RUN <build-command>

# ---- Runtime Stage ----
FROM <runtime-image>
COPY --from=builder /src/<artifact> /<dest>
EXPOSE <port>
CMD [<entrypoint>]

Step 3: Apply Language-Specific Patterns

Node.js (pruned node_modules)

FROM node:22-bookworm AS builder
WORKDIR /src
COPY package.json package-lock.json ./
RUN npm ci
COPY . .
RUN npm run build && npm prune --omit=dev

FROM node:22-bookworm-slim
RUN groupadd -r app && useradd -r -g app app
WORKDIR /app
COPY --from=builder /src/dist ./dist
COPY --from=builder /src/node_modules ./node_modules
COPY --from=builder /src/package.json .
USER app
EXPOSE 3000
CMD ["node", "dist/index.js"]

Python (virtualenv copy)

FROM python:3.12-bookworm AS builder
WORKDIR /src
RUN python -m venv /opt/venv
ENV PATH="/opt/venv/bin:$PATH"
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .

FROM python:3.12-slim-bookworm
COPY --from=builder /opt/venv /opt/venv
ENV PATH="/opt/venv/bin:$PATH"
WORKDIR /app
COPY --from=builder /src .
RUN groupadd -r app && useradd -r -g app app
USER app
EXPOSE 8000
CMD ["python", "app.py"]

Go (static binary to scratch)

FROM golang:1.23-bookworm AS builder
WORKDIR /src
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /server ./cmd/server

FROM scratch
COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
COPY --from=builder /server /server
EXPOSE 8080
ENTRYPOINT ["/server"]

Rust (static musl binary)

FROM rust:1.82-bookworm AS builder
RUN apt-get update && apt-get install -y musl-tools && rm -rf /var/lib/apt/lists/*
RUN rustup target add x86_64-unknown-linux-musl
WORKDIR /src
COPY Cargo.toml Cargo.lock ./
RUN mkdir src && echo "fn main() {}" > src/main.rs \
    && cargo build --release --target x86_64-unknown-linux-musl \
    && rm -rf src
COPY . .
RUN touch src/main.rs && cargo build --release --target x86_64-unknown-linux-musl

FROM scratch
COPY --from=builder /src/target/x86_64-unknown-linux-musl/release/myapp /myapp
EXPOSE 8080
ENTRYPOINT ["/myapp"]

Expected: Final image contains only the runtime and compiled artifacts.

On failure: Check COPY --from=builder paths. Use docker build --target builder to debug the build stage.

Step 4: Choose Runtime Base

Note: Alpine uses musl libc. Some Python wheels and Node native modules may not work. Prefer -slim (glibc) for interpreted languages.

Step 5: Build Args Across Stages

ARG APP_VERSION=0.0.0

FROM golang:1.23 AS builder
ARG APP_VERSION
RUN go build -ldflags="-X main.version=${APP_VERSION}" -o /server .

FROM gcr.io/distroless/static
COPY --from=builder /server /server
ENTRYPOINT ["/server"]

Build with: docker build --build-arg APP_VERSION=1.2.3 .

Note: ARG before FROM is global. Each stage must re-declare ARG to use it.

Step 6: Compare Image Sizes

# Build both variants
docker build -t myapp:fat --target builder .
docker build -t myapp:slim .

# Compare sizes
docker images --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}" | grep myapp

Expected: Production image is 50-90% smaller than the build stage.

Validation

• docker build completes for all stages
• Final image does not contain build tools (compilers, dev headers)
• docker run works correctly from the slim image
• Image size is significantly reduced vs single-stage
• COPY --from=builder paths are correct
• No source code leaks into the production image

Common Pitfalls

• Missing runtime libraries: Compiled code may need shared libraries (libc, libssl). Test the slim image thoroughly.
• Broken COPY --from paths: The artifact path must match exactly. Use docker build --target builder then docker run --rm builder ls /path to debug.
• Alpine musl issues: Native Node.js addons and some Python packages fail on Alpine. Use -slim instead.
• Global ARG scope: An ARG declared before FROM is available to FROM lines only. Re-declare inside each stage that needs it.
• Forgetting CA certificates: scratch has no certificates. Copy /etc/ssl/certs/ca-certificates.crt from the builder or use distroless.

Related Skills

• create-dockerfile - single-stage general Dockerfiles
• create-r-dockerfile - R-specific Dockerfiles with rocker images
• optimize-docker-build-cache - layer caching and BuildKit features
• setup-compose-stack - compose configurations using multi-stage images