Multi-Stage Builds — Dramatically Smaller Images

What You'll Learn

Beginner

• What multi-stage builds are and why they matter
• How to separate build tools from runtime
• Real examples in Go, Java, and Node.js

The Problem Multi-Stage Solves

Without multi-stage, your production image includes build tools, source code, and temporary artifacts — none needed at runtime.

The Solution: Multiple Stages

A multi-stage Dockerfile has multiple FROM lines. Each FROM starts a new stage. You COPY --from only what you need.

Example: Go Application

# Stage 1: Build
FROM golang:1.21 AS builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o myapp .

# Stage 2: Runtime
FROM alpine:3.18
RUN apk add --no-cache ca-certificates
WORKDIR /app
COPY --from=builder /app/myapp .
CMD ["./myapp"]

Result: ~22 MB image instead of ~800 MB.

Example: Node.js Application

# Stage 1: Build
FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: Runtime (only production deps)
FROM node:18-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY --from=builder /app/dist ./dist
CMD ["node", "dist/server.js"]

Practical Exercise