Lesson 3: Docker Architecture Explained

Understanding the components of Docker is crucial for troubleshooting and advanced usage.

Docker operates using a client-server architecture. The client talks to the daemon (server), which does the heavy lifting.

1. The Docker Client (CLI)

• This is the primary way users interact with Docker.
• It's a command-line tool (docker).
• The Client sends commands (like docker run, docker build, docker pull) to the Docker Daemon.
• It can communicate with the Daemon locally or remotely.

2. The Docker Daemon (Engine)

• The server component, often called dockerd.
• It manages the Docker objects: images, containers, networks, and volumes.
• It listens for API requests from the Client.
• Key responsibilities include:
  • Building images.
  • Running, stopping, and managing containers.
  • Handling image storage and networking.

3. Docker Registries

• A Registry is a centralized location where Docker Images are stored.
• Docker Hub is the default public registry.
• When you run docker pull nginx, Docker pulls the Nginx image from Docker Hub.
• When you run docker push, you are sending your custom image to a registry.

Flow of a Command (docker run) (Analogy)

1. You (Client): Send the instruction to start a container.
2. Daemon (Engine): Receives the instruction.
3. Daemon (Image Management): Checks local storage for the requested image.
4. Daemon (Registry Interaction): If not found, pulls the image from Docker Hub.
5. Daemon (Container Management): Creates and starts a new container instance based on the image.

This architecture ensures that managing containers and images is separated from the user interface, providing efficiency and scalability.