Understanding the C4 Model for Software Architecture

 

Understanding the C4 Model for Software Architecture

The C4 Model is a structured approach to visualizing and documenting software architecture. Created by Simon Brown, it organizes system design into four hierarchical levels: Context, Container, Component, and Code. This model helps both technical and non-technical stakeholders understand the structure of a system at varying levels of detail.

Why Use the C4 Model?

Traditional UML (Unified Modeling Language) diagrams can be complex and difficult to maintain. The C4 Model simplifies architectural descriptions, making them more accessible and easier to manage. It allows teams to:
✅ Clearly communicate architecture across different roles.
✅ Maintain flexibility across monolithic and microservices-based architectures.
✅ Focus on essential details without unnecessary complexity.

The Four Levels of the C4 Model with Sample Diagrams

1. Context Diagram (High-Level Overview)

  • Purpose: Shows how the system fits within its environment.
  • Audience: Business stakeholders, architects, and developers.
  • Elements:
    • The software system being designed.
    • Users interacting with it.
    • External dependencies such as APIs or third-party services.

Example: Online Banking System (Context Level)

📌 Scenario: A customer interacts with an Online Banking System, which communicates with an External Payment System and Bank Database.

Diagram Representation (Conceptual Example):

+----------------------+
| Customer            |
| (User)              |
+----------------------+
         |
         v
+----------------------+
| Online Banking App  |
| (System)            |
+----------------------+
   |            |
   v            v
+----------------------+     +----------------------+
| Bank Database       | <--->| External Payment API |
+----------------------+     +----------------------+

🛠 How to Create: Use Draw.io, Structurizr, or PlantUML (C4_Context) to generate a visual version.

2. Container Diagram (System Breakdown)

  • Purpose: Shows the major parts (containers) within the system.
  • Audience: Architects, developers, and DevOps engineers.
  • Elements:
    • Web applications, databases, APIs, and microservices.
    • Interactions between these components.

Example: Online Banking System (Container Level)

📌 Scenario: The banking system consists of a Web App, Mobile App, API Service, and a Database.

Diagram Representation (Conceptual Example):

+----------------------+
| Customer            |
+----------------------+
   |     |
   v     v
+----------------------+       +----------------------+
| Mobile App          | <--->  | Web Application     |
+----------------------+       +----------------------+
   |                              |
   v                              v
+--------------------------------------------------+
| Banking API (Handles transactions & authentication) |
+--------------------------------------------------+
   |
   v
+----------------------+
| Bank Database       |
+----------------------+

🛠 How to Create: Use Structurizr, Draw.io, or PlantUML (C4_Container).

3. Component Diagram (Detailed Breakdown of a Container)

  • Purpose: Breaks down a single container into its internal components.
  • Audience: Developers and architects.
  • Elements:
    • Services/modules inside a container.
    • Interactions between these services.

Example: API Service in Online Banking (Component Level)

📌 Scenario: The Banking API consists of three main components:

  1. Authentication Service – Handles user login.
  2. Transaction Service – Processes payments and transfers.
  3. Notification Service – Sends email/SMS notifications.

Diagram Representation (Conceptual Example):

+--------------------------------------------------+
| Banking API                                     |
|--------------------------------------------------|
|  +-----------------+   +-----------------+      |
|  | Authentication  |   | Transaction     |      |
|  | Service        |   | Service         |      |
|  +-----------------+   +-----------------+      |
|         |                     |                |
|         v                     v                |
|  +-----------------+   +-----------------+      |
|  | Notification   |   | Database Access |      |
|  | Service       |   | Layer           |      |
|  +-----------------+   +-----------------+      |
+--------------------------------------------------+

🛠 How to Create: Use Structurizr, Draw.io, or PlantUML (C4_Component).

4. Code Diagram (Deep Dive into Code Level - Optional)

  • Purpose: Shows how a single component is implemented at the code level.
  • Audience: Developers.
  • Elements:
    • Classes, methods, and interactions inside a component.

Example: Code-Level Breakdown of Authentication Service

📌 Scenario: The Authentication Service has three key classes:

  1. UserController – Handles HTTP requests.
  2. AuthService – Processes authentication logic.
  3. UserRepository – Manages database queries.

Diagram Representation (Conceptual Example):

+----------------------+
| UserController       |
+----------------------+
        |
        v
+----------------------+
| AuthService         |
+----------------------+
        |
        v
+----------------------+
| UserRepository      |
+----------------------+

🛠 How to Create: Use PlantUML (C4_Code) or class diagram tools like UMLet.

Tools for Creating C4 Diagrams

There are several tools available for drawing C4 Model diagrams:

  1. Structurizr – Best for C4 Model diagrams.
  2. Draw.io (diagrams.net) – Free and easy to use.
  3. PlantUML – Supports text-based diagram generation.
  4. Microsoft Visio – Suitable for enterprise use.

Conclusion

The C4 Model is an effective method for visualizing and documenting software architecture. By using Context, Container, Component, and Code diagrams, teams can ensure clear communication and better understanding of system structures. Whether designing a new system or documenting an existing one, the C4 Model is a valuable tool for software development.

Would you like a real generated diagram? Let me know which level you'd like, and I can create one!

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