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Generate an optimized Dockerfile for the current project.

Steps

1. Detect Project Type

  • Read package.json, pyproject.toml, go.mod, Cargo.toml, or equivalent to determine the language and framework.
  • Identify the build command and output directory.
  • Identify runtime dependencies vs. build-only dependencies.

2. Choose Base Image

  • Node.js: node:22-alpine for runtime, node:22 for build if native modules are needed.
  • Python: python:3.12-slim for runtime, full image for build if compilation is needed.
  • Go: golang:1.23-alpine for build, gcr.io/distroless/static-debian12 for runtime.
  • Rust: rust:1.82-slim for build, debian:bookworm-slim or scratch for runtime.

3. Multi-Stage Build

# Stage 1: Build
FROM <build-image> AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --production=false
COPY . .
RUN npm run build

# Stage 2: Runtime
FROM <runtime-image>
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
USER node
CMD ["node", "dist/index.js"]

4. Optimization Checklist

  • Copy dependency files first, then source code (layer caching).
  • Use .dockerignore to exclude: .git, node_modules, dist, .env, tests, docs.
  • Run as non-root user.
  • Set NODE_ENV=production or equivalent.
  • Add health check: HEALTHCHECK CMD curl -f http://localhost:3000/health || exit 1.
  • Pin base image versions with digest for reproducibility.
  • Minimize layers by combining related RUN commands.

5. Generate .dockerignore

Create or update .dockerignore with sensible defaults for the project type.

Rules

  • Always use multi-stage builds to minimize image size.
  • Never copy .env files or secrets into the image.
  • Run as a non-root user in the final stage.
  • Include a HEALTHCHECK instruction.
  • Keep the final image under 200MB for typical web applications.
  • Test the built image locally with docker build -t app . && docker run -p 3000:3000 app.