Cheatsheet

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Cheatsheet#

Docker is a platform for developing, shipping, and running applications in containers. Created in 2013, Docker has revolutionized application deployment by enabling developers to package applications with all their dependencies into standardized units (containers) for software development. Containers are lightweight, portable, and ensure consistent behavior across different environments.

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Container Lifecycle Management

# Start a container
docker run -d --name myapp nginx:latest
docker run -it ubuntu bash  # Interactive mode

# Container operations
docker start myapp
docker stop myapp
docker restart myapp
docker pause myapp
docker unpause myapp

# Remove containers
docker rm myapp  # Remove stopped container
docker rm -f myapp  # Force remove running container
docker container prune  # Remove all stopped containers

# View containers
docker ps  # List running containers
docker ps -a  # List all containers
docker stats  # Container resource usage

Image Management

# Image operations
docker pull nginx:latest
docker push myregistry/myapp:v1
docker images  # List all images
docker rmi nginx:latest  # Remove image
docker image prune  # Remove unused images
docker image prune -a  # Remove all unused images

# Build image from Dockerfile
docker build -t myapp:v1 .
docker build --no-cache -t myapp:v1 .

# Save and load images
docker save myapp:v1 > myapp.tar
docker load < myapp.tar

# Tag images
docker tag myapp:v1 myregistry/myapp:latest

Network Management

# Network operations
docker network create mynetwork
docker network ls
docker network rm mynetwork

# Connect containers to network
docker run --network mynetwork myapp
docker network connect mynetwork myapp
docker network disconnect mynetwork myapp

# Network drivers
docker network create --driver bridge mybridge
docker network create --driver overlay myoverlay
docker network create --driver host myhost

# Network inspection
docker network inspect mynetwork

Volume Management

# Volume operations
docker volume create myvolume
docker volume ls
docker volume rm myvolume
docker volume prune

# Mount volume in container
docker run -v myvolume:/app/data myapp
docker run --mount source=myvolume,target=/app/data myapp

# Bind mounts
docker run -v $(pwd):/app myapp
docker run --mount type=bind,source=$(pwd),target=/app myapp

# Temporary mounts
docker run --tmpfs /app/temp myapp

Container Resource Management

# Memory limits
docker run --memory="512m" myapp
docker run --memory-swap="1g" myapp

# CPU limits
docker run --cpus=".5" myapp  # Use half CPU
docker run --cpu-shares=512 myapp

# Resource constraints
docker run --pids-limit=100 myapp
docker run --device-read-bps=/dev/sda:1mb myapp

# Update running container
docker update --cpus=".75" myapp
docker update --memory="1g" myapp

Docker Compose

# docker-compose.yml
version: '3.8'
services:
webapp:
    build: .
    ports:
    - "3000:3000"
    environment:
    - NODE_ENV=production
    volumes:
    - ./data:/app/data
    depends_on:
    - db

db:
    image: postgres:13
    environment:
    - POSTGRES_PASSWORD=secret
    volumes:
    - db-data:/var/lib/postgresql/data

volumes:
db-data:

# Commands
docker-compose up -d
docker-compose down
docker-compose logs -f
docker-compose ps
docker-compose exec webapp bash

Logging and Debugging

# View logs
docker logs myapp
docker logs -f myapp  # Follow logs
docker logs --tail 100 myapp
docker logs --since 1h myapp

# Debug containers
docker exec -it myapp bash
docker exec myapp ps aux
docker top myapp
docker inspect myapp

# Copy files
docker cp myapp:/app/log.txt ./log.txt
docker cp ./config.json myapp:/app/

Security Best Practices

# Run as non-root user
docker run --user 1000:1000 myapp

# Read-only root filesystem
docker run --read-only myapp

# Security options
docker run --security-opt no-new-privileges myapp
docker run --cap-drop ALL --cap-add NET_BIND_SERVICE myapp

# Scan images
docker scan myapp:latest

Multi-stage Builds

# Build stage
FROM node:16 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

# Production stage
FROM node:16-slim
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY package*.json ./
RUN npm install --production
CMD ["npm", "start"]

Health Checks and Auto-healing

# Dockerfile health check
HEALTHCHECK --interval=30s --timeout=3s \
CMD curl -f http://localhost/ || exit 1

# Docker run health check
docker run --health-cmd="curl -f localhost:3000 || exit 1" \
        --health-interval=30s \
        --health-retries=3 \
        --health-timeout=3s \
        myapp

# Check container health
docker inspect --format='{{.State.Health.Status}}' myapp

Pro Tips

  • Use .dockerignore to exclude unnecessary files

  • Always specify image versions, avoid ‘latest’ tag

  • Use multi-stage builds to reduce final image size

  • Implement proper logging strategies

  • Use docker-compose for development environments

  • Regularly update base images for security

  • Cache build dependencies efficiently

  • Use environment variables for configuration

  • Implement proper backup strategies for volumes

  • Monitor container resource usage

  • Use container orchestration for production (Kubernetes/Swarm)

  • Keep images minimal - only include what’s necessary

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