Why your Docker images are too big (and how to fix it)

FROM node:20
WORKDIR /app
COPY . .
RUN npm install
CMD ["node", "server.js"]

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --production
COPY . .
CMD ["node", "server.js"]

# Build stage
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Production stage
FROM node:20-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/package*.json ./
RUN npm ci --production && npm cache clean --force
CMD ["node", "dist/server.js"]

node_modules
.git
.env*
*.md
tests
coverage
.github
docker-compose*.yml

# Bad: any code change invalidates npm install cache
COPY . .
RUN npm ci

# Good: npm install only reruns when package.json changes
COPY package*.json ./
RUN npm ci --production
COPY . .

# Go example
FROM golang:1.22-alpine AS builder
WORKDIR /app
COPY . .
RUN CGO_ENABLED=0 go build -o /server .

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

docker images myapp
docker history myapp:latest  # See each layer's size
docker scout quickview myapp  # CVE scan + size analysis