C4 Model Diagram

C4 Model Diagram

Create C4 diagrams to communicate architecture at multiple abstraction levels.

Context

You are creating architecture diagrams. Use C4 model for consistent representation. Start at highest level (context), zoom in progressively (container, component, code). Read architecture decisions and system structure.

Domain Context

Based on Simon Brown's C4 model:

• Context Diagram: System in environment. Shows external systems, users, data flows. Answers: "What is this system?"
• Container Diagram: Major building blocks (web app, database, API, message queue). Answers: "What's inside the system?"
• Component Diagram: Internal structure of container. Shows responsibilities, communication. Answers: "How is [container] organized?"
• Code Diagram: Class diagram for specific component. Shows classes, methods, relationships. Answers: "What does [component] contain?"

Instructions

1. Draw Context Diagram: Rectangle for your system. External systems (payment provider, email service). Actors (user, admin). Label data flows. Answers "What does this system do?"

2. Draw Container Diagram: Inside system rectangle, show containers (web app, API, database, cache). Interfaces between containers. Technology choices (PostgreSQL, Redis). Answers "What technology?"

3. Draw Component Diagram: Pick one container (API). Inside, show components (auth service, payment service, order service). Responsibilities, communication patterns.

4. Draw Code Diagram: For complex component, show classes, methods. Use standard UML or pseudo-code. Limit to critical logic; don't over-document.

5. Keep Diagrams Current: As architecture evolves, update diagrams. Outdated diagrams mislead teams. Use tools (draw.io, Structurizr, Miro) that allow collaboration and versioning.

Anti-Patterns

• One Massive Diagram: Try to show everything in one diagram. Result: unreadable, overwhelming. Guard: Use C4 levels; zoom progressively.
• Diagrams Without Legend: Assume readers know what symbols mean. Result: confusion. Guard: Label technologies, responsibilities, data flows clearly.
• Outdated Diagrams: Never update as system evolves. Result: teams follow wrong architecture. Guard: Update during architecture reviews; treat as living document.
• Too Much Detail Too Early: Start with code diagram. Result: lost in details before understanding system shape. Guard: Start at context; zoom in gradually; leave code diagram optional.

Further Reading

• The C4 Model for Software Architecture by Simon Brown — foundational reference
• Software Architecture in Practice by Len Bass et al. — visualization best practices
• Communicating Software Architecture — architecture documentation patterns