What is Docker?
Docker is a platform for developing, shipping, and running applications in containers.
Containers vs Virtual Machines
| Feature | Containers | VMs |
|---|---|---|
| Size | Megabytes | Gigabytes |
| Startup | Seconds | Minutes |
| OS | Shared kernel | Full OS |
| Isolation | Process-level | Hardware-level |
Why Docker?
- Consistency: Same environment everywhere
- Isolation: Apps don't interfere with each other
- Portability: Run anywhere Docker runs
- Efficiency: Lightweight and fast
Docker Architecture
┌─────────────────────────────────────┐
│ Docker Client │
│ (docker commands) │
└──────────────┬──────────────────────┘
│
┌──────────────▼──────────────────────┐
│ Docker Daemon │
│ (manages containers/images) │
└──────────────┬──────────────────────┘
│
┌──────────────▼──────────────────────┐
│ Container Runtime │
└─────────────────────────────────────┘
Key Concepts
- Image: Blueprint for containers
- Container: Running instance of an image
- Registry: Storage for images (Docker Hub)
- Dockerfile: Instructions to build an image