Docker Fundamentals

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Docker is a platform that uses containerization technology to package applications and their dependencies into lightweight, portable containers.

What is Docker?

Docker allows you to:

• Package applications with all dependencies
• Run applications consistently across different environments
• Isolate applications from each other
• Scale applications efficiently

Core Concepts

Images

• Read-only templates used to create containers
• Built from Dockerfile instructions
• Stored in registries (Docker Hub, etc.)

Containers

• Running instances of Docker images
• Lightweight and isolated
• Share the host OS kernel

Dockerfile

• Text file with instructions to build an image
• Defines the environment and dependencies
• Version controlled with your application

Essential Commands

# Build an image
docker build -t myapp .

# Run a container
docker run -d -p 8080:80 myapp

# List running containers
docker ps

# Stop a container
docker stop container_id

# Remove containers and images
docker rm container_id
docker rmi image_id

Best Practices

1. Use official base images
2. Minimize layer count
3. Use .dockerignore files
4. Don’t run as root user
5. Use multi-stage builds for production

Next Steps

• Learn Docker Compose for multi-container applications
• Explore Kubernetes for orchestration
• Study container security best practices