/dockerfile

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`.