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dockerfile-generation

DevOps & Security
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Generate production-ready multi-stage Dockerfiles per ecosystem with best practices. Use when the user needs a Dockerfile, asks about containerization, or when no Dockerfile exists in the repository.

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How to use this skill

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  2. Copy the prompt below and paste it into your agent.
  3. Review the proposed files and risks before you approve installation.
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Source SKILL.md: https://github.com/nixopus/nixopus/blob/HEAD/api/skills/dockerfile-generation/SKILL.md

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Dockerfile Generation

Generate production Dockerfiles using multi-stage builds. Always optimize for small image size, layer caching, and security.

General rules

  • Always use multi-stage builds (builder + runtime)
  • Pin base image versions (e.g. node:20-alpine, not node:latest)
  • Use Alpine or slim variants for runtime
  • Copy dependency files first, install, then copy source (layer caching)
  • Run as non-root user in production
  • Set NODE_ENV=production or equivalent
  • Include EXPOSE directive for the detected port
  • Use .dockerignore to exclude node_modules, .git, dist, __pycache__

Node.js

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

FROM node:20-alpine
WORKDIR /app
RUN addgroup -S app && adduser -S app -G app
COPY --from=builder /app/package*.json ./
RUN npm ci --omit=dev
COPY --from=builder /app/dist ./dist
USER app
EXPOSE 3000
CMD ["node", "dist/index.js"]

Variations:

  • Next.js: Use output: 'standalone' in next.config.js. Copy .next/standalone and .next/static.
  • Vite/CRA (static): Build in Node, serve with nginx:alpine. Copy dist/ or build/ to /usr/share/nginx/html.
  • pnpm: Replace npm ci with corepack enable && pnpm install --frozen-lockfile.
  • yarn: Replace npm ci with yarn install --frozen-lockfile.
  • Bun: Use oven/bun:1-alpine as base.

Go

FROM golang:1.22-alpine AS builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 GOOS=linux go build -o /app/server ./cmd/server

FROM alpine:3.19
RUN addgroup -S app && adduser -S app -G app
COPY --from=builder /app/server /server
USER app
EXPOSE 8080
CMD ["/server"]

Use scratch instead of alpine if the binary has no external dependencies and doesn't need a shell.

Python

FROM python:3.12-slim AS builder
WORKDIR /app
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

FROM python:3.12-slim
WORKDIR /app
RUN useradd -r -s /bin/false app
COPY --from=builder /usr/local/lib/python3.12/site-packages /usr/local/lib/python3.12/site-packages
COPY --from=builder /usr/local/bin /usr/local/bin
COPY . .
USER app
EXPOSE 8000
CMD ["gunicorn", "app:app", "--bind", "0.0.0.0:8000"]

Variations:

  • FastAPI: CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]
  • Django: CMD ["gunicorn", "project.wsgi:application", "--bind", "0.0.0.0:8000"]
  • Poetry: Copy pyproject.toml and poetry.lock, use poetry install --no-dev.

Rust

FROM rust:1.77-alpine AS builder
WORKDIR /app
RUN apk add musl-dev
COPY Cargo.toml Cargo.lock ./
RUN mkdir src && echo "fn main() {}" > src/main.rs
RUN cargo build --release
COPY src ./src
RUN touch src/main.rs && cargo build --release

FROM alpine:3.19
RUN addgroup -S app && adduser -S app -G app
COPY --from=builder /app/target/release/<binary_name> /app
USER app
EXPOSE 8080
CMD ["/app"]

Java (Maven)

FROM maven:3.9-eclipse-temurin-21 AS builder
WORKDIR /app
COPY pom.xml ./
RUN mvn dependency:go-offline
COPY src ./src
RUN mvn package -DskipTests

FROM eclipse-temurin:21-jre-alpine
WORKDIR /app
RUN addgroup -S app && adduser -S app -G app
COPY --from=builder /app/target/*.jar app.jar
USER app
EXPOSE 8080
CMD ["java", "-jar", "app.jar"]

Static sites (nginx)

For any frontend that produces a dist/ or build/ directory:

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

FROM nginx:alpine
COPY --from=builder /app/dist /usr/share/nginx/html
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

Checklist before generating

  1. Read the manifest file to confirm ecosystem and framework
  2. Check for existing .dockerignore — if missing, generate one
  3. Detect the actual build output directory (may not be dist/)
  4. Detect the actual start command from scripts.start or framework defaults
  5. Detect the correct port from code or config
  6. Check if the app needs build-time env vars (e.g. NEXT_PUBLIC_*)

Related Skills

  • deployment-analysis — Run first to determine the ecosystem, framework, port, and build commands before generating a Dockerfile
  • env-detection — Identify build-time vs runtime env vars that need ARG/ENV directives in the Dockerfile
  • compose-setup — If the app needs a database or other services alongside the Dockerfile