Docker Essentials

Container Inspection & Debugging

Viewing logs

# Show logs
docker logs container_name

# Follow logs (like tail -f)
docker logs -f container_name

# Last 100 lines
docker logs --tail 100 container_name

# Logs with timestamps
docker logs -t container_name

Executing commands

# Execute command in running container
docker exec container_name ls -la

# Interactive shell
docker exec -it container_name bash

# Execute as specific user
docker exec -u root -it container_name bash

# Execute with environment variable
docker exec -e VAR=value container_name env

Inspection

# Inspect container details
docker inspect container_name

# Get specific field (JSON path)
docker inspect -f '{{.NetworkSettings.IPAddress}}' container_name

# View container stats
docker stats

# View specific container stats
docker stats container_name

# View processes in container
docker top container_name

Image Management

Building images

# Build from Dockerfile
docker build -t myapp:1.0 .

# Build with custom Dockerfile
docker build -f Dockerfile.dev -t myapp:dev .

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

# Build without cache
docker build --no-cache -t myapp .

Managing images

# List images
docker images

# Pull image from registry
docker pull nginx:latest

# Tag image
docker tag myapp:1.0 myapp:latest

# Push to registry
docker push myrepo/myapp:1.0

# Remove image
docker rmi image_name

# Remove unused images
docker image prune

# Remove all unused images
docker image prune -a

Docker Compose

Basic operations

# Start services
docker-compose up

# Start in background
docker-compose up -d

# Stop services
docker-compose down

# Stop and remove volumes
docker-compose down -v

# View logs
docker-compose logs

# Follow logs for specific service
docker-compose logs -f web

# Scale service
docker-compose up -d --scale web=3

Service management

# List services
docker-compose ps

# Execute command in service
docker-compose exec web bash

# Restart service
docker-compose restart web

# Rebuild service
docker-compose build web

# Rebuild and restart
docker-compose up -d --build

Networking

# List networks
docker network ls

# Create network
docker network create mynetwork

# Connect container to network
docker network connect mynetwork container_name

# Disconnect from network
docker network disconnect mynetwork container_name

# Inspect network
docker network inspect mynetwork

# Remove network
docker network rm mynetwork

Volumes

# List volumes
docker volume ls

# Create volume
docker volume create myvolume

# Inspect volume
docker volume inspect myvolume

# Remove volume
docker volume rm myvolume

# Remove unused volumes
docker volume prune

# Run with volume
docker run -v myvolume:/data -d app

System Management

# View disk usage
docker system df

# Clean up everything unused
docker system prune

# Clean up including unused images
docker system prune -a

# Clean up including volumes
docker system prune --volumes

# Show Docker info
docker info

# Show Docker version
docker version

Common Workflows

Development container:

docker run -it --rm \
  -v $(pwd):/app \
  -w /app \
  -p 3000:3000 \
  node:18 \
  npm run dev

Database container:

docker run -d \
  --name postgres \
  -e POSTGRES_PASSWORD=secret \
  -e POSTGRES_DB=mydb \
  -v postgres-data:/var/lib/postgresql/data \
  -p 5432:5432 \
  postgres:15

Quick debugging:

# Shell into running container
docker exec -it container_name sh

# Copy file from container
docker cp container_name:/path/to/file ./local/path

# Copy file to container
docker cp ./local/file container_name:/path/in/container

Multi-stage build:

# Dockerfile
FROM node:18 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

FROM nginx:alpine
COPY --from=builder /app/dist /usr/share/nginx/html

Useful Flags

docker run flags:

• -d: Detached mode (background)
• -it: Interactive terminal
• -p: Port mapping (host:container)
• -v: Volume mount
• -e: Environment variable
• --name: Container name
• --rm: Auto-remove on exit
• --network: Connect to network

docker exec flags:

• -it: Interactive terminal
• -u: User
• -w: Working directory

Tips

• Use .dockerignore to exclude files from build context
• Combine RUN commands in Dockerfile to reduce layers
• Use multi-stage builds to reduce image size
• Always tag your images with versions
• Use --rm for one-off containers
• Use docker-compose for multi-container apps
• Clean up regularly with docker system prune

Documentation

Official docs: https://docs.docker.com/ Dockerfile reference: https://docs.docker.com/engine/reference/builder/ Compose file reference: https://docs.docker.com/compose/compose-file/