Add Docker

Use this skill when the user asks to dockerize, containerize, or add Docker support to an application.

Steps

1. Detect the runtime — inspect package.json, requirements.txt, go.mod, Cargo.toml, etc. to determine the language and runtime.

2. Create a multi-stage Dockerfile

   For Node.js (example):

   FROM node:20-alpine AS base
   
   FROM base AS deps
   WORKDIR /app
   COPY package.json package-lock.json ./
   RUN npm ci --omit=dev
   
   FROM base AS build
   WORKDIR /app
   COPY package.json package-lock.json ./
   RUN npm ci
   COPY . .
   RUN npm run build
   
   FROM base AS runner
   WORKDIR /app
   ENV NODE_ENV=production
   COPY --from=deps /app/node_modules ./node_modules
   COPY --from=build /app/.next ./.next
   COPY --from=build /app/public ./public
   COPY --from=build /app/package.json ./
   EXPOSE 3000
   CMD ["npm", "start"]
   

   Adapt for the detected framework — adjust the build output directory, entry command, and base image.

3. Create .dockerignore

   node_modules
   .next
   .git
   .env*
   *.md
   

4. Create docker-compose.yml (if the app has dependencies like a database or Redis):

   services:
     app:
       build: .
       ports:
         - "3000:3000"
       env_file: .env
       depends_on:
         - db
     db:
       image: postgres:16-alpine
       environment:
         POSTGRES_DB: app
         POSTGRES_USER: postgres
         POSTGRES_PASSWORD: postgres
       volumes:
         - pgdata:/var/lib/postgresql/data
   volumes:
     pgdata:
   

5. Add npm scripts (optional)

   {
     "docker:build": "docker build -t myapp .",
     "docker:run": "docker compose up"
   }
   

Notes

• Use Alpine-based images to minimize image size.
• Never copy .env files into the image — use env_file or runtime injection.
• For monorepos, use a .dockerignore that excludes sibling packages not needed by the target app.
• Add a HEALTHCHECK instruction for production deployments.