Docker CLI Guide

Docker is a containerization platform that packages applications and dependencies into isolated containers. This guide provides essential workflows and quick references for common Docker operations.

Quick Start

# Check Docker installation
docker --version

# Run your first container
docker run hello-world

# Run interactive container
docker run -it ubuntu bash

# Run container in background
docker run -d nginx

# List running containers
docker ps

# Stop a container
docker stop container_name

Common Workflows

Workflow 1: Build and Run an Application

# Create Dockerfile in your project directory
# Build image
docker build -t myapp:latest .

# Run container with port mapping
docker run -d -p 8080:80 --name myapp myapp:latest

# View logs
docker logs -f myapp

# Access container shell
docker exec -it myapp bash

Workflow 2: Development with Hot Reload

# Run with volume mount for live code updates
docker run -d \
  -p 8080:80 \
  -v $(pwd)/src:/app/src \
  --name myapp-dev \
  myapp:dev

# Watch logs in real-time
docker logs -f myapp-dev

# Restart after configuration changes
docker restart myapp-dev

Workflow 3: Multi-Container Application with Docker Compose

# Create docker-compose.yml with services
# Start all services
docker compose up -d

# View service logs
docker compose logs -f

# Scale a service
docker compose up -d --scale api=3

# Stop all services
docker compose down

# Stop and remove volumes
docker compose down -v

Workflow 4: Push Image to Registry

# Login to registry
docker login

# Build and tag image
docker build -t myapp:latest .
docker tag myapp:latest username/myapp:v1.0.0
docker tag myapp:latest username/myapp:latest

# Push to registry
docker push username/myapp:v1.0.0
docker push username/myapp:latest

Workflow 5: Debug Container Issues

# Check container status
docker ps -a

# View container logs
docker logs container_name

# Inspect container details
docker inspect container_name

# Run interactive shell for debugging
docker run -it --entrypoint /bin/bash myapp:latest

# Check container resource usage
docker stats container_name

Decision Tree

When to use which command:

• To run a new container: Use docker run with appropriate flags
• To execute commands in running container: Use docker exec -it container_name bash
• To build an image: Use docker build -t name:tag .
• To manage multiple services: Use docker compose up/down
• To check container status: Use docker ps or docker ps -a
• To view logs: Use docker logs -f container_name
• To clean up resources: Use docker system prune or specific prune commands
• For detailed command syntax: See Commands Reference
• For complex scenarios: See Common Patterns
• For troubleshooting: See Troubleshooting Guide

Common Patterns

Running Containers with Options

# With environment variables
docker run -e ENV_VAR=value -e API_KEY=secret myapp

# With resource limits
docker run --memory=512m --cpus=1.5 myapp

# With restart policy
docker run --restart=unless-stopped myapp

# With custom network
docker run --network mynetwork myapp

# With volume mount
docker run -v mydata:/app/data myapp

Container-to-Container Communication

# Create custom network
docker network create myapp-network

# Run containers on same network
docker run -d --name database --network myapp-network postgres:15
docker run -d --name app --network myapp-network -p 8080:80 myapp

# Containers can now access each other by name
# Example: app can connect to database using hostname "database"

Data Persistence

# Create named volume
docker volume create myapp-data

# Use volume in container
docker run -d -v myapp-data:/var/lib/postgresql/data postgres:15

# Backup volume data
docker run --rm \
  -v myapp-data:/data \
  -v $(pwd):/backup \
  ubuntu tar czf /backup/backup.tar.gz /data

Troubleshooting

Common Issues:

1. Container exits immediately

   • Solution: Check logs with docker logs container_name
   • See: Container Won't Start

2. Can't access service on published port

   • Quick fix: Verify port mapping with docker port container_name
   • See: Container Running But Not Accessible

3. Permission denied errors

   • Quick fix: Run with user flag docker run -u $(id -u):$(id -g)
   • See: Permission Denied Errors

4. Disk space issues

   • Quick fix: Clean up with docker system prune -a --volumes
   • See: Disk Space Issues

5. Network connectivity issues

   • Quick fix: Check container network with docker network inspect bridge
   • See: Network Issues

For detailed troubleshooting steps, see the Troubleshooting Guide.

Reference Files

Load as needed for detailed information:

• Commands Reference - Complete CLI command documentation with all flags and options. Use when you need exact syntax or flag details for any Docker command.

• Common Patterns - Real-world patterns and workflows for development, multi-stage builds, networking, volumes, CI/CD, security, and production deployments. Use for implementing specific workflows or integrations.

• Troubleshooting Guide - Detailed error messages, diagnosis steps, and resolution strategies for container, image, network, volume, performance, and system issues. Use when encountering errors or unexpected behavior.

When to use each reference:

• Use Commands Reference when you need exact syntax, flag combinations, or comprehensive command documentation
• Use Common Patterns for implementing multi-container setups, production configurations, or CI/CD pipelines
• Use Troubleshooting when containers won't start, services are unreachable, or you encounter permission/network/performance issues

Resources

• Official Docs: https://docs.docker.com
• Docker Hub: https://hub.docker.com
• GitHub: https://github.com/docker
• Community: https://forums.docker.com