Docker Architecture

How Docker Works

Docker uses a client-server architecture with three main components.

The Three Components

  ┌─────────────────────┐
  │    Docker Client     │  ← You (docker CLI)
  │  docker run, build   │
  └──────────┬──────────┘
             │ REST API
  ┌──────────▼──────────┐
  │   Docker Daemon      │  ← dockerd (background service)
  │  Builds, runs,       │
  │  manages containers  │
  └──────────┬──────────┘
             │
  ┌──────────▼──────────┐
  │   containerd +       │  ← Low-level container runtime
  │   runc               │
  └─────────────────────┘

Key Concepts

• Image — A read-only template with instructions for creating a container. Think of it as a blueprint.
• Container — A running instance of an image. You can create many containers from one image.
• Registry — A storage for images. Docker Hub is the default public registry.
• Dockerfile — A text file with step-by-step instructions to build an image.

Data Flow

  1. You write a Dockerfile
  2. docker build → Docker daemon builds an image
  3. docker run → Docker daemon creates a container from that image
  4. Container runs your app in isolation
  5. docker push → Share image to a registry
  6. Someone pulls your image and runs it

  Dockerfile → Image → Container → Running App