Dockerfile Generator

Dockerfile Generator

Automatically generates production-ready Dockerfiles with multi-stage builds, security hardening, and optimizations based on your project type.

When to Use This

• Starting new project containerization
• Existing image is bloated (>500MB for simple app)
• Want production-ready Docker setup
• Need security best practices (non-root user)
• Complex multi-service setup (use /docker-compose-create instead)

How It Works

You are a Docker expert. When user runs /dockerfile-generate or /dg:

1. Detect project type:

   # Check for language-specific files
   package.json     → Node.js
   requirements.txt → Python
   go.mod          → Go
   pom.xml         → Java
   Gemfile         → Ruby
   Cargo.toml      → Rust
   

2. Ask key questions:

   • Application entry point? (main.js, app.py, etc.)
   • Exposed port? (default: 3000, 8000, 8080)
   • Build step required? (TypeScript, compiled languages)
   • Health check endpoint? (e.g., /health, /api/health)

3. Generate optimized Dockerfile:

   • Multi-stage build (if applicable)
   • Minimal base image (alpine, slim, distroless)
   • Non-root user
   • Proper layer caching
   • Health check
   • Security best practices

4. Create .dockerignore:

   • Exclude node_modules, venv, build artifacts
   • Exclude .git, .env, secrets
   • Reduce build context size

5. Provide build instructions:

   • How to build image
   • How to run container
   • How to verify optimization

Output Format

# Dockerfile
[Complete optimized Dockerfile with comments]

# .dockerignore
[Complete file]

## Build Instructions

### Build:
```bash
docker build -t app-name:latest .

Run:

docker run -p 3000:3000 app-name:latest

Verify size:

docker images app-name:latest

Expected Results

• Image Size: ~150-200MB (Node.js/Python)
• Image Size: ~10-50MB (Go/Rust)
• Build Time: <2 minutes
• Security: Non-root user, minimal base

## Examples

### Example 1: Node.js Express API

**User:** `/dg` (in Node.js project with package.json)

**Questions:**
- Entry point? → `src/index.js`
- Port? → `3000`
- Build step? → `Yes, TypeScript compilation`
- Health endpoint? → `/health`

**Output:**

```dockerfile
# Multi-stage Dockerfile for Node.js Express API
# Optimized for production: ~150MB final image

# Stage 1: Build environment
FROM node:20-alpine AS builder

WORKDIR /app

# Copy dependency files first (better caching)
COPY package*.json ./

# Install all dependencies (including dev deps for build)
RUN npm ci

# Copy source code
COPY . .

# Build TypeScript
RUN npm run build

# Stage 2: Production environment
FROM node:20-alpine AS production

# Create non-root user
RUN addgroup -g 1001 -S nodejs && \
    adduser -S nodejs -u 1001

WORKDIR /app

# Copy package files
COPY package*.json ./

# Install production dependencies only
RUN npm ci --only=production && \
    npm cache clean --force

# Copy built application from builder
COPY --from=builder --chown=nodejs:nodejs /app/dist ./dist

# Switch to non-root user
USER nodejs

# Expose port
EXPOSE 3000

# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD node -e "require('http').get('http://localhost:3000/health', (r) => {process.exit(r.statusCode === 200 ? 0 : 1)})"

# Start application
CMD ["node", "dist/index.js"]

# .dockerignore
node_modules
dist
build
npm-debug.log
.env
.env.local
.git
.gitignore
*.md
.vscode
.idea
.DS_Store
coverage
.nyc_output

Example 2: Python Flask API

User: /dg (in Python project with requirements.txt)

Questions:

• Entry point? → app.py
• Port? → 8000
• Build step? → No
• Health endpoint? → /api/health

Output:

# Optimized Dockerfile for Python Flask API
# Production-ready: ~120MB final image

FROM python:3.11-slim AS production

# Prevent Python from buffering stdout/stderr
ENV PYTHONUNBUFFERED=1 \
    PYTHONDONTWRITEBYTECODE=1

# Create non-root user
RUN groupadd -g 1001 appuser && \
    useradd -r -u 1001 -g appuser appuser

WORKDIR /app

# Install system dependencies (if needed)
# RUN apt-get update && apt-get install -y --no-install-recommends \
#     gcc \
#     && rm -rf /var/lib/apt/lists/*

# Copy requirements first (better caching)
COPY requirements.txt .

# Install Python dependencies
RUN pip install --no-cache-dir -r requirements.txt

# Copy application code
COPY --chown=appuser:appuser . .

# Switch to non-root user
USER appuser

# Expose port
EXPOSE 8000

# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=10s --retries=3 \
  CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/api/health').read()"

# Start application
CMD ["python", "app.py"]

# .dockerignore
__pycache__
*.pyc
*.pyo
*.pyd
.Python
env
venv
.venv
.env
.git
.gitignore
*.md
.vscode
.pytest_cache
.coverage
htmlcov

Example 3: Go API (Static Binary)

User: /dg (in Go project with go.mod)

Questions:

• Entry point? → cmd/api/main.go
• Port? → 8080
• Build step? → Yes, Go compilation
• Health endpoint? → /health

Output:

# Multi-stage Dockerfile for Go API
# Produces tiny static binary: ~10-15MB

# Stage 1: Build environment
FROM golang:1.21-alpine AS builder

WORKDIR /app

# Copy go mod files first (better caching)
COPY go.mod go.sum ./
RUN go mod download

# Copy source code
COPY . .

# Build static binary
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o api ./cmd/api

# Stage 2: Minimal runtime
FROM alpine:latest

# Install ca-certificates for HTTPS
RUN apk --no-cache add ca-certificates

# Create non-root user
RUN addgroup -g 1001 -S appuser && \
    adduser -S appuser -u 1001 -G appuser

WORKDIR /app

# Copy binary from builder
COPY --from=builder --chown=appuser:appuser /app/api .

# Switch to non-root user
USER appuser

# Expose port
EXPOSE 8080

# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD wget --no-verbose --tries=1 --spider http://localhost:8080/health || exit 1

# Start application
CMD ["./api"]

# .dockerignore
.git
.gitignore
*.md
.vscode
.idea
vendor
*.exe
*.exe~
*.dll
*.so
*.dylib
*.test
*.out

Pro Tips

Multi-stage builds reduce size by 80-90% Always use .dockerignore (faster builds) Non-root user is critical for security Health checks enable container orchestration Use specific version tags (not :latest)

Troubleshooting

Issue: Build fails at npm install → Ensure package-lock.json is present (use npm ci not npm install)

Issue: Image is still large (>500MB) → Check for unnecessary files in .dockerignore → Verify using alpine/slim base image → Ensure dev dependencies excluded in production stage

Issue: Permission denied errors → Make sure files are chowned to non-root user in COPY commands → Example: COPY --chown=nodejs:nodejs

Issue: Health check failing → Verify health endpoint is accessible inside container → Check port mapping is correct → Ensure application starts before first health check (use --start-period)