dockerfile

Dockerfile Skill

Overview

Best practices and patterns for writing efficient, secure, and maintainable Dockerfiles.

Capabilities

• Multi-stage builds
• Layer optimization
• Security hardening
• Size optimization
• Development vs Production configurations

---

Basic Dockerfile Structure

# Use official base image with specific version
FROM node:18-alpine

# Set working directory
WORKDIR /app

# Copy dependency files
COPY package*.json ./

# Install dependencies
RUN npm ci --only=production

# Copy application code
COPY . .

# Expose port
EXPOSE 3000

# Run application
CMD ["node", "server.js"]

---

Multi-Stage Builds

Node.js Example

# Build stage
FROM node:18-alpine AS builder

WORKDIR /app

COPY package*.json ./
RUN npm ci

COPY . .
RUN npm run build

# Production stage
FROM node:18-alpine AS production

WORKDIR /app

# Copy only necessary files from builder
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY package*.json ./

# Use non-root user
USER node

EXPOSE 3000

CMD ["node", "dist/server.js"]

Go Example

# Build stage
FROM golang:1.21-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

# Production stage
FROM alpine:latest

RUN apk --no-cache add ca-certificates

WORKDIR /root/

COPY --from=builder /app/server ./

EXPOSE 8080

CMD ["./server"]

Python Example

# Build stage
FROM python:3.11-slim AS builder

WORKDIR /app

RUN python -m venv /opt/venv
ENV PATH="/opt/venv/bin:$PATH"

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Production stage
FROM python:3.11-slim

WORKDIR /app

COPY --from=builder /opt/venv /opt/venv

ENV PATH="/opt/venv/bin:$PATH"
ENV PYTHONUNBUFFERED=1

COPY . .

EXPOSE 8000

CMD ["python", "app.py"]

---

Best Practices

1. Use Specific Base Image Tags

# ❌ Bad: Using 'latest' tag
FROM node:latest

# ✅ Good: Using specific version
FROM node:18.17.0-alpine

# ✅ Also good: Using digest for reproducibility
FROM node:18-alpine@sha256:a1e8...