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Docker

Docker cheat sheet with essential commands for containers, images, volumes, networks, Docker Compose, and orchestration examples.

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Container Management

Running Containers

Start and run Docker containers with various options

bash
# Run container
docker run nginx
docker run -d nginx                     # Detached mode
docker run -it ubuntu bash              # Interactive
docker run --name web nginx             # Named container

# Port mapping
docker run -p 8080:80 nginx            # Host:Container
docker run -P nginx                     # Random ports

# Volume mounting
docker run -v /host:/container nginx   # Bind mount
docker run -v myvolume:/data nginx     # Named volume

# Environment
docker run -e NODE_ENV=prod node       # Single var
docker run --env-file .env node        # From file
💡 Use -d for background containers
⚠️ Always name containers for easier management
📌 Use --rm for temporary containers
✅ Set resource limits in production

Container State Management

Control container lifecycle - start, stop, restart, and remove

bash
# List containers
docker ps                    # Running only
docker ps -a                 # All containers
docker ps -q                 # Only IDs

# Start/Stop/Restart
docker start container_name
docker stop container_name
docker restart container_name

# Remove containers
docker rm container_name
docker rm -f container_name  # Force remove

# Clean up
docker container prune       # Remove stopped
💡 docker ps -a shows stopped containers too
⚠️ Use -f flag carefully to force remove
📌 Container prune removes all stopped containers
✅ Always stop before removing unless using -f

Container Inspection & Logs

Debug and inspect running containers for troubleshooting

bash
# View logs
docker logs container_name
docker logs -f container_name           # Follow
docker logs --tail 50 container_name    # Last 50 lines

# Execute commands
docker exec container_name ls
docker exec -it container_name bash

# Inspect container
docker inspect container_name

# Copy files
docker cp container:/path/file local/path
docker cp local/file container:/path/
💡 Use -f to follow logs in real-time
📌 docker exec -it for interactive sessions
⚡ Inspect with --format for specific fields
✅ Copy files without stopping container

Executing Commands in Containers

Run commands inside running containers with docker exec and copy files with docker cp

bash
# Run a command in a running container
docker exec my-container ls /app

# Open an interactive shell
docker exec -it my-container sh
docker exec -it my-container bash

# Copy files between host and container
docker cp my-container:/app/logs ./logs
docker cp ./config.yml my-container:/app/config.yml
💡 docker exec -it opens an interactive terminal — use sh for Alpine, bash for Debian/Ubuntu
⚡ Use docker cp to quickly grab log files or inject config without rebuilding
📌 docker stats shows live resource usage — essential for debugging memory/CPU issues
🟢 docker exec -d runs the command in the background without attaching to it
execcpdebug

Image Management

Building Images

Build Docker images from Dockerfiles with various options

bash
# Build image
docker build -t myapp .
docker build -t myapp:v1 .
docker build -f Dockerfile.dev -t myapp:dev .

# Build arguments
docker build --build-arg VERSION=1.0 -t myapp .

# Build options
docker build --no-cache -t myapp .
docker build --pull -t myapp .
💡 Use .dockerignore to exclude files
⚡ BuildKit provides advanced features
📌 Multi-stage builds reduce image size
✅ Always tag images with versions

Image Operations

Manage Docker images - pull, push, tag, and remove

bash
# List images
docker images
docker image ls

# Pull images
docker pull nginx
docker pull nginx:alpine

# Push images
docker push myregistry/myapp:v1

# Tag images
docker tag myapp:latest myapp:v1.0
docker tag myapp registry/myapp:latest

# Remove images
docker rmi image_name
docker image prune              # Dangling images
💡 Use specific tags instead of latest
⚠️ Prune regularly to save disk space
📌 Save images for offline transfer
✅ Always login before pushing

Image Registry

Work with Docker registries and manage image distribution

bash
# Login to registry
docker login
docker login docker.io
docker login -u user -p pass registry.io

# Logout
docker logout
docker logout registry.io

# Search images
docker search nginx
docker search --limit 10 nginx
docker search --filter stars=100 nginx

# Registry operations
docker pull registry.io/namespace/image:tag
docker push registry.io/namespace/image:tag

# Local registry
docker run -d -p 5000:5000 --name registry registry:2
docker tag myapp localhost:5000/myapp
docker push localhost:5000/myapp
🔒 Always use HTTPS for production registries
💡 Tag images with registry URL
📌 Local registry useful for testing
✅ Implement authentication for private registries

Dockerfile

Write Dockerfiles to build custom images with all the key instructions

Dockerfile Instructions

The essential Dockerfile commands for building images

dockerfile
FROM node:22-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --production
COPY . .
ENV NODE_ENV=production
EXPOSE 3000
CMD ["node", "server.js"]
💡 Always use specific image tags (node:22-alpine) not "latest" — reproducible builds
⚡ Copy package.json first, then npm install, then copy source — maximizes Docker layer cache
📌 ARG is build-time only; ENV persists into the running container — know the difference
🟢 Run as a non-root USER in production — it only takes 2 lines and prevents privilege escalation
dockerfilebuildinstructions

Multi-Stage Builds

Use multiple FROM stages to create small, optimized production images

dockerfile
# Build stage
FROM node:22-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Production stage — only the output
FROM node:22-alpine AS production
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY --from=build /app/node_modules ./node_modules
CMD ["node", "dist/server.js"]
💡 Multi-stage builds keep dev tools (compilers, build deps) out of the final image
⚡ Go apps can use FROM scratch for the final stage — just the binary, ~10MB total
📌 COPY --from=stagename copies files from a previous stage into the current one
🟢 Use --target to build a specific stage: docker build --target build .
multi-stagebuildoptimization

.dockerignore

Exclude files from the build context to speed up builds and avoid leaking secrets

bash
# .dockerignore
node_modules
.git
.env
*.md
dist
.DS_Store
💡 Without .dockerignore, Docker sends EVERYTHING in the directory to the build daemon
⚡ Always ignore node_modules — they get reinstalled with npm ci inside the image
📌 Ignore .env files to prevent secrets from being baked into the image
🟢 Same syntax as .gitignore — supports wildcards, negation (!important.md), and comments
dockerignorebuildsecurity

Volumes & Networks

Volume Management

Create and manage Docker volumes for persistent data storage

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

# Use volumes
docker run -v myvolume:/data nginx
docker run -v /host/path:/container/path nginx
💡 Named volumes persist data between containers
📌 Bind mounts for development, volumes for production
⚠️ Prune removes all unused volumes
✅ Backup important volumes regularly

Network Management

Configure Docker networks for container communication

bash
# Network operations
docker network create mynetwork
docker network ls
docker network inspect bridge
docker network rm mynetwork
docker network prune

# Container networking
docker run --network=mynetwork nginx
docker network connect mynetwork container
docker network disconnect mynetwork container
💡 Containers on same network can communicate by name
🔒 Use internal networks for security
📌 Bridge is default, overlay for Swarm
✅ Custom networks provide better isolation

Docker Compose

Compose Basics

Essential Docker Compose commands for multi-container applications

bash
# Start services
docker compose up
docker compose up -d            # Detached
docker compose up --build       # Rebuild

# Stop services
docker compose down
docker compose down -v          # Remove volumes
docker compose stop

# Logs and status
docker compose ps
docker compose logs
docker compose logs -f service

# Execute commands
docker compose exec service bash
docker compose run service command
💡 Use -d for background operation
⚡ --scale for horizontal scaling
📌 -f to specify custom compose files
✅ Always use down -v to clean volumes

Compose Configuration

Full compose.yml reference with depends_on, healthcheck, profiles, watch, and more

yaml
services:
  app:
    build: .
    ports:
      - "3000:3000"
    depends_on:
      db:
        condition: service_healthy
    environment:
      DATABASE_URL: postgres://user:pass@db:5432/mydb

  db:
    image: postgres:17-alpine
    volumes:
      - db-data:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD", "pg_isready"]
      interval: 10s
      timeout: 5s
      retries: 5

volumes:
  db-data:
💡 depends_on with condition: service_healthy waits until the dependency passes its healthcheck
⚡ Compose Watch syncs files without rebuilding — use action: sync for source, action: rebuild for deps
📌 Profiles let you define optional services (debug tools, admin panels) that only start when requested
🟢 Use env_file to load .env files — keeps secrets out of compose.yml and version control

System & Cleanup

System Management

Monitor and manage Docker system resources and information

bash
# System info
docker info
docker version
docker system df

# Cleanup
docker system prune
docker system prune -a
docker container prune
docker image prune
docker volume prune
docker network prune

# Stats
docker stats
docker stats --no-stream
💡 Regular pruning prevents disk issues
⚠️ Prune -a removes all unused images
📌 Use filters to control what gets pruned
✅ Monitor disk usage with system df

Debugging & Troubleshooting

Debug containers and resolve common Docker issues

bash
# Debug running container
docker logs container_name
docker logs -f --tail 50 container_name
docker exec -it container_name sh

# Inspect details
docker inspect container_name
docker inspect image_name

# Debug build
docker build --no-cache --progress=plain .

# Check processes
docker top container_name

# File changes
docker diff container_name
💡 nicolaka/netshoot has many network tools
🔍 Use --progress=plain for detailed build output
📌 Override entrypoint to debug failed containers
✅ Always check logs first when debugging