Docker is a containerization platform that packages applications and their dependencies into lightweight, portable containers. Unlike virtual machines that virtualize entire operating systems, Docker containers share the host OS kernel while maintaining application isolation.
Key differences:

• Resource Usage: Containers use fewer resources as they share the host kernel
• Startup Time: Containers start in seconds vs minutes for VMs
• Portability: Containers run consistently across different environments
• Isolation: VMs provide stronger isolation but at higher overhead cost

Docker follows a client-server architecture with these main components:

• Docker Client: Command-line interface that communicates with Docker daemon
• Docker Daemon (dockerd): Background service managing containers, images, and networks
• Docker Images: Read-only templates used to create containers
• Docker Containers: Running instances of Docker images
• Docker Registry: Storage for Docker images (e.g., Docker Hub)
• Docker Engine: Complete containerization platform combining daemon, REST API, and CLI

A Docker image is a read-only template containing application code, runtime, libraries, and dependencies. A Docker container is a running instance of an image.
Key differences:

• Images are immutable blueprints; containers are mutable runtime environments
• Images are stored; containers are executed
• Multiple containers can be created from a single image
• Changes to containers don't affect the original image
  Example:

# Image exists as a template
docker images
# Container is created and runs from image
docker run nginx

Docker provides several key benefits:

• Consistency: "Works on my machine" problem solved through consistent environments
• Portability: Applications run anywhere Docker is installed
• Scalability: Easy horizontal scaling of containerized applications
• Resource Efficiency: Lower overhead compared to traditional VMs
• Development Speed: Faster development cycles with instant environment setup
• Microservices Support: Ideal for breaking monoliths into microservices
• CI/CD Integration: Seamless integration with DevOps pipelines

Use the docker run command to create and start a container from an image:

# Basic container creation
docker run nginx
# Run with custom name and port mapping
docker run --name my-nginx -p 8080:80 nginx
# Run in background (detached mode)
docker run -d --name web-server nginx
# Run interactively
docker run -it ubuntu bash