adding-docker

Add Docker

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

Steps

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

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):

```yaml
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:

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.

About this skill

Steps

Notes