The C4 model provides a structured approach to architecture diagrams. After using C4 in production, here’s how to document architecture effectively.

C4 Model Levels

Level 1: System Context

Shows:

  • System and users
  • External systems
  • High-level view
┌─────────┐
│  Users  │
└────┬────┘
     │
┌────▼────────────┐
│  E-Commerce     │
│     System      │
└────┬────────────┘
     │
┌────▼────┐  ┌─────┐
│Payment  │  │Email│
│Gateway  │  │Svc  │
└─────────┘  └─────┘

Level 2: Container Diagram

Shows:

  • Applications
  • Databases
  • File systems
┌─────────────┐
│  Web App    │
└──────┬──────┘
       │
   ┌───┴───┬────────┬────────┐
   │       │        │        │
┌──▼──┐ ┌──▼──┐ ┌──▼──┐ ┌───▼──┐
│ API │ │Auth │ │Order│ │Email │
│ Svc │ │ Svc │ │ Svc │ │ Svc  │
└──┬──┘ └──┬──┘ └──┬──┘ └──┬───┘
   │       │        │       │
┌──▼──┐ ┌──▼──┐ ┌──▼──┐
│Postg│ │Redis│ │SQS  │
│res  │ │     │ │     │
└─────┘ └─────┘ └─────┘

Level 3: Component Diagram

Shows:

  • Components within container
  • Relationships
  • Technologies

Level 4: Code Diagram

Shows:

  • Classes
  • Functions
  • Implementation details

Best Practices

  1. Start with context - System context first
  2. Use consistent notation - Standard symbols
  3. Keep it simple - Don’t over-complicate
  4. Update regularly - Keep current
  5. Use tools - Structurizr, Draw.io
  6. Document decisions - Link to ADRs
  7. Multiple views - Different perspectives
  8. Team collaboration - Shared understanding

Conclusion

The C4 model enables:

  • Clear documentation
  • Multiple abstraction levels
  • Team alignment
  • Maintainable diagrams

Start with system context, then drill down. The model shown here documents production architectures effectively.

C4 Model from January 2022, covering architecture visualization.