Writing a Dockerfile

Writing a Dockerfile

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

Multi-stage: Node.js example

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

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.
• A .dockerignore excludes node_modules, .git, .env.
• The final image uses a lightweight base (alpine, slim) whenever possible.