# Docker

**Docker** is a containerization platform that packages your application and its dependencies into a lightweight, portable unit called a container. Run `docker run` to start a container from an image; it starts instantly and includes everything your app needs—no "works on my machine" problems.

An **image** is a blueprint: a layered filesystem snapshot plus metadata. A **container** is a running instance of an image, with its own isolated filesystem, network, and environment. Build images from a Dockerfile, run containers from images, and share images via a registry (Docker Hub, private registries, etc.).

```bash
$ docker build -t myapp .     # build an image from Dockerfile
$ docker run myapp            # run a container from an image
$ docker push myapp           # push image to registry
$ docker pull myapp           # pull image from registry
```

Containers are ephemeral by default—data disappears when they stop. Use volumes for persistent storage, networks to link containers, and Compose to orchestrate multi-container apps.

## Concepts

 1. [[docker-images|Images]]
 2. [[docker-containers|Containers]]
 3. [[docker-dockerfile|Dockerfile]]
 4. [[docker-building|Building images]]
 5. [[docker-running|Running containers]]
 6. [[docker-volumes|Volumes]]
 7. [[docker-networks|Networks]]
 8. [[docker-registries|Registries]]
 9. [[docker-pulling-and-pushing|Pulling and pushing]]
 10. [[docker-tagging|Tagging]]
 11. [[docker-layers|Layers]]
 12. [[docker-entrypoint-and-cmd|Entrypoint and CMD]]
 13. [[docker-environment-variables|Environment variables]]
 14. [[docker-ports|Ports and networking]]
 15. [[docker-compose|Compose]]