# Writing a Dockerfile

Source : https://webgune.cloud/en-us/docs/docker-dockerfile · Mis à jour le 2026-10-27

# Writing a Dockerfile

A few principles that keep your images lightweight and your builds fast on Webgune.

## Multi-stage: Node.js example

```dockerfile
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

FROM node:20-alpine AS runner
WORKDIR /app
ENV NODE_ENV=production
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
CMD ["node", "dist/server.js"]
```

The `builder` stage contains the compilation tools and the npm cache; only the strict minimum needed is copied into the final stage, which drastically reduces the size of the delivered image.

## Multi-stage: Go example

```dockerfile
FROM golang:1.22-alpine AS builder
WORKDIR /app
COPY go.* ./
RUN go mod download
COPY . .
RUN go build -o server .

FROM alpine:latest
COPY --from=builder /app/server /server
CMD ["/server"]
```

## Checklist before pushing

- [ ] The application listens on `0.0.0.0:$PORT`, not on a hardcoded port.
- [ ] No secret is copied into the image: everything goes through [environment variables](/docs/variables-environnement).
- [ ] A `.dockerignore` excludes `node_modules`, `.git`, `.env`.
- [ ] The final image uses a lightweight base (`alpine`, `slim`) whenever possible.