Docker Architecture

Understanding Docker architecture helps you know how Docker works under the hood. Docker uses a client-server architecture made up of several core components.

Core Components of Docker Architecture

How Docker Client and Daemon Communicate

When you type a Docker command like docker run nginx, here is what happens:

1. The Docker Client sends the command to the Docker Daemon via REST API.
2. The Docker Daemon checks if the image exists locally.
3. If not found, it pulls the image from Docker Hub (Registry).
4. The Daemon creates and starts a Container from the image.
5. Output is returned back to the Docker Client.

# Docker Client sends this command
docker run nginx

# Docker Daemon pulls image if not available
# Unable to find image locally
# Pulling from library/nginx

Docker Objects

Images

An image is a read-only template that contains the OS, app code, runtime, libraries, and environment variables.

# List all local images
docker images

# Pull an image from Docker Hub
docker pull ubuntu

Containers

A container is a running instance of an image. It has its own filesystem, network, and process space.

# Run a container
docker run -it ubuntu bash

# List running containers
docker ps

# List all containers (including stopped)
docker ps -a

Docker Registry

Docker Hub is the default public registry. You can also set up a private registry.

# Push image to Docker Hub
docker push yourusername/myapp

# Pull image from Docker Hub
docker pull yourusername/myapp

Docker Namespaces & Control Groups

Docker uses Linux features under the hood:

• Namespaces — Isolate containers (PID, network, file system, user).
• Control Groups (cgroups) — Limit CPU, memory, and I/O usage per container.
• Union File System — Layers of read-only image + writable container layer.

Docker Architecture Diagram (Text)

[ Docker CLI (Client) ]
        |
        | REST API
        v
[ Docker Daemon (dockerd) ]
        |
   _____|_____
  |           |
[Images]  [Containers]
        |
        v
[ Docker Registry (Docker Hub) ]

Summary

• Docker uses a client-server model.
• The Docker Daemon manages all images, containers, networks, and volumes.
• The Docker Client sends commands to the Daemon via REST API.
• Docker Hub is the default registry to store and pull images.