Stage 1: Build (command)

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 ```dockerfile # 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`.