Docker Basics

1. Course Introduction:

Docker is a containerization platform that packages an application with the libraries, runtime and configuration it needs. This makes
application behavior more consistent across development, testing and production.
Key Point: Package once and run consistently across environments.

2. What are Containers?

A container is a lightweight, isolated runtime environment for an application. Containers share the host operating-system kernel
instead of carrying a complete guest OS, so they generally start faster and use fewer resources than virtual machines.
Key Point: A container is an isolated application process, not a complete VM.

3. How Docker Works:

The Docker Client accepts commands such as docker run. Docker Engine performs the requested work: pulling images, creating
containers and managing their lifecycle. Images are commonly downloaded from a registry such as Docker Hub.
Key Point: CLI -> Docker Engine -> Image -> Container.
Docker CLI
docker run
>
Docker Engine
manages resources
>
Container
running app

4. Containers vs Virtual Machines:

Both provide isolation. A VM includes a complete guest operating system, while containers share the host OS kernel. Containers are
therefore attractive for fast application delivery and microservices.

Containers                                                                       Virtual Machines
Share host OS kernel                                                        Include a guest OS
Lightweight and fast                                                          Higher resource usage
Great for portable apps                                                     Useful for full OS isolation

5. Images and Registries:

A Docker image is a read-only package used to create containers. A container is a running instance of an image. A registry stores and
distributes images; Docker Hub is a commonly used public registry.
Key Point: Image = blueprint | Container = running instance | Registry = image store.

6. Basic Docker Commands:  Common beginner commands for managing Docker images and containers:
Command:                                          Purpose:

docker run nginx                 Create and start a container.

docker ps                             List running containers.

docker ps -a                         List all containers.
docker images                     List local images.
docker pull nginx                Download an image.
docker stop                         Stop a running container.
docker start                        Start a stopped container.
docker restart                     Restart a container.

docker logs                        View container logs.
docker exec -it /bin/sh      Open a shell in a running container.
docker rm                           Remove a stopped container.
docker rmi                          Remove a local image.

Quick Practice:

$ docker pull nginx
$ docker run -d --name web -p 8080:80 nginx
$ docker ps
$ docker logs web
$ docker stop web
$ docker rm web

Course Summary:

You now understand containers, Docker architecture, containers vs VMs, images and registries, and the essential Docker CLI commands used in basic day-to-day workflows.