Multi stage builds

Multi-Stage Builds

Use multi-stage Docker builds to produce minimal, secure production images by separating build-time tooling from runtime dependencies.

When to Use

• User needs to reduce Docker image size
• User ships compilers or build tools in production images
• User asks about distroless or alpine base images
• User wants faster Docker builds with cache mounts
• User needs different images for dev, test, and production

Core Patterns

Node.js Builder Pattern

Separate TypeScript compilation and dependency installation from the runtime image.

# ---------- Stage 1: Install dependencies ----------
FROM node:20-alpine AS deps
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci

# ---------- Stage 2: Build ----------
FROM deps AS builder
COPY tsconfig.json ./
COPY src/ src/
RUN npm run build && npm prune --omit=dev

# ---------- Stage 3: Production ----------
FROM gcr.io/distroless/nodejs20-debian12
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY --from=builder /app/package.json ./
EXPOSE 3000
CMD ["dist/index.js"]

Result: ~150MB image instead of ~1GB with full Node.js + dev dependencies.

Go Static Binary

Go compiles to a single static binary, making scratch or distroless ideal.

FROM golang:1.22-alpine AS builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
    go build -ldflags="-s -w" -o /server ./cmd/server

FROM gcr.io/distroless/static-debian12
COPY --from=builder /server /server
USER nonroot:nonroot
ENTRYPOINT ["/server"]

Result: ~10-20MB image with zero OS packages and no shell for attackers to exploit.

Python with Virtual Environment

Isolate Python dependencies in a virtualenv, then copy only the venv to the runtime image.

FROM python:3.12-slim AS builder
WORKDIR /app
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
WORKDIR /app
RUN groupadd -r app && useradd -r -g app app
COPY --from=builder /opt/venv /opt/venv
COPY --from=builder /app /app
ENV PATH="/opt/venv/bin:$PATH"
USER app
EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Cache Mounts for Faster Builds

Use BuildKit cache mounts to persist package manager caches across builds, avoiding repeated downloads.

FROM node:20-alpine AS builder
WORKDIR /app
COPY package.json package-lock.json ./
RUN --mount=type=cache,target=/root/.npm \
    npm ci
COPY . .
RUN npm run build

FROM rust:1.77-alpine AS rust-builder
WORKDIR /app
COPY Cargo.toml Cargo.lock ./
COPY src/ src/
RUN --mount=type=cache,target=/usr/local/cargo/registry \
    --mount=type=cache,target=/app/target \
    cargo build --release && \
    cp target/release/myapp /usr/local/bin/myapp

Build Args for Conditional Stages

Use build args to customize builds without separate Dockerfiles.

ARG BUILD_ENV=production

FROM node:20-alpine AS base
WORKDIR /app
COPY package.json package-lock.json ./

FROM base AS deps-production
RUN npm ci --omit=dev

FROM base AS deps-development
RUN npm ci

FROM deps-${BUILD_ENV} AS deps

FROM node:20-alpine AS final
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .

Build with: docker build --build-arg BUILD_ENV=development -t myapp:dev .

Target-Based Development Workflow

Use named stages with --target for different environments from a single Dockerfile.

FROM node:20-alpine AS base
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci

FROM base AS development
COPY . .
CMD ["npm", "run", "dev"]

FROM base AS test
COPY . .
RUN npm run lint && npm test

FROM base AS builder
COPY . .
RUN npm run build && npm prune --omit=dev

FROM gcr.io/distroless/nodejs20-debian12 AS production
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
CMD ["dist/index.js"]

docker build --target development -t myapp:dev .
docker build --target test -t myapp:test .
docker build --target production -t myapp:prod .

Anti-Patterns

• Copying build tools into production: Never include compilers, package managers, or dev headers in the final stage. They waste space and increase attack surface.
• Using ubuntu or debian for runtime: Prefer alpine, slim, distroless, or scratch. A full Debian base adds 100-200MB of unnecessary packages.
• Not separating dependency install from code copy: If you COPY everything before npm ci, every source code change invalidates the dependency cache.
• Ignoring --mount=type=cache: Without cache mounts, every build re-downloads all dependencies from scratch. Enable BuildKit and use cache mounts.
• Single Dockerfile per environment: Use --target and build args instead of maintaining separate Dockerfiles for dev, test, and prod.

Quick Reference

Base Image	Size	Shell	Use Case
scratch	0 MB	No	Go static binaries
distroless/static	~2 MB	No	Static binaries, max security
distroless/cc	~20 MB	No	C/C++ apps needing libc
distroless/nodejs20	~130 MB	No	Node.js production
alpine	~7 MB	Yes	When you need a shell
debian-slim	~80 MB	Yes	When you need apt packages

# Enable BuildKit (required for cache mounts)
export DOCKER_BUILDKIT=1

# Build specific target
docker build --target production -t myapp:prod .

# Check final image size
docker images myapp:prod