Understanding Software Architecture: A Journey Through C4 Model with Real-World Examples

The Architecture Dilemma: A Story

It’s Monday morning, and Sansrithi, a tech lead at a growing software company, is facing a familiar challenge. Her team has just kicked off a new project, and she needs to explain the system architecture to three different groups:

• The development team needs technical details to start coding
• The project manager needs to understand dependencies and timelines
• The business stakeholders need to grasp the system’s capabilities

Sansrithi pulls up her whiteboard marker and starts drawing boxes and arrows. By the third revision, the diagram is a maze of lines, and she can see the confusion in everyone’s eyes. Sound familiar?

This scenario plays out in companies worldwide every day. It highlights a fundamental challenge in software development:

How do we effectively communicate software architecture to different audiences?

The Communication Challenge

The Multi-Audience Problem

Imagine trying to explain your city to three different people:

• A tourist who wants to know about main attractions
• A civil engineer who needs to understand the infrastructure
• A postal worker who needs to know every street and address

Each needs a different level of detail. The same applies to software architecture:

Why Traditional Documentation Falls Short

Traditional documentation methods often suffer from:

1. The Single-View Problem

• One diagram trying to serve all purposes
• Either too detailed or too abstract

2. The Maintenance Nightmare

• Documents become outdated quickly
• No clear connection to actual code

3. Communication Gap

• Technical jargon confuses non-technical stakeholders
• Oversimplification frustrates developers

Evolution of Architecture Documentation

The Journey So Far

1. 1990s: UML Dominance

• Promised standardization
• Became too complex
• Often disconnected from real code

2. 2000s: Informal Approaches

• Box and line diagrams
• Whiteboard photos
• Lack of consistency

3. 2010s: Agile Impact

• Minimal documentation
• Tribal knowledge
• Communication challenges in distributed teams

The Need for Something Better

A good architecture documentation system should:

• Scale with complexity
• Serve multiple audiences
• Stay connected to the code
• Be easy to maintain
• Support agile development

Enter the C4 Model

What is C4?

The C4 model, created by Simon Brown, is like a map system for your code. Just as you can zoom into a map from country level to street level, C4 lets you zoom into your architecture from high-level context to low-level code.

The Four C’s

1. Context (L1) — Your system on a map
2. Containers (L2) — The high-level building blocks
3. Components (L3) — Inside each container
4. Code (L4) — The implementation details

Detailed Dive into C4 Levels

We will take the E-com app as an example to explore it further.

Level 1: Context — The Big Picture

Think of Context diagrams like a satellite view of your system. They answer the question:

“How does this system fit into the world?”

https://youtube.com/@codefarm0

Key Elements to Include:

• Users (people who use your system)
• System (your system)
• External systems (things your system interacts with)

Best Practices:

• Keep it simple — aim for 1-page view
• Focus on people and software systems
• Don’t include technical details
• Use clear, business-focused language

Level 2: Containers — The Building Blocks

Containers break down your system into high-level technical blocks. Think of them as separately deployable units.

https://youtube.com/@codefarm0

What Constitutes a Container:

• Web applications
• Mobile apps
• Databases
• File systems
• Microservices

Common Container Types in Modern Systems:

1. Frontend Containers

• Web Applications (React, Angular)
• Mobile Apps (iOS, Android)
• Desktop Applications

2. Backend Containers

• API Services
• Processing Jobs
• Message Queues

3. Data Containers

• Databases
• Cache Systems
• File Storage

Level 3: Components — The Internal Workings

Components show how containers are built. They represent the major structural building blocks within each container.

https://youtube.com/@codefarm0

Component Identification Tips:

• Look for clear boundaries in your code
• Consider business capabilities
• Think about reusable modules
• Identify major patterns (MVC, CQRS, etc.)

Level 4: Code — The Implementation Details

And last part goes to the code.

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    private String description;
    private BigDecimal price;
    private Integer stockQuantity;
    private String sellerId;
    
    @OneToMany(mappedBy = "product")
    private List<ProductImage> images;
    
    @ManyToOne
    private Category category;
    
    // Getters, setters, and business methods
}

@Service
public class ProductService {
    @Autowired
    private ProductRepository productRepository;
    
    @Autowired
    private InventoryService inventoryService;
    
    @Autowired
    private PriceService priceService;
    
    @Autowired
    private CacheManager cacheManager;
    
    @Autowired
    private EventPublisher eventPublisher;
    
    @Transactional
    public Product createProduct(ProductDTO productDTO) {
        // Validation logic
        Product product = new Product();
        // Map DTO to entity
        product = productRepository.save(product);
        
        // Update cache
        cacheManager.put(product.getId(), product);
        
        // Publish event
        eventPublisher.publishProductCreated(product);
        
        return product;
    }
    
    // Other business methods
}

Above are for examples, no need to show case the complete code in the diagrams, here we directly refer to the code repository.

Code Level Best Practices:

• Show only significant classes
• Focus on relationships and patterns
• Include key methods and properties
• Link to actual codebase when possible

Practical Implementation Guide

Choosing the Right Tools

1. Diagram Creation Tools:

• PlantUML (free, text-based)
• Structurizr (dedicated C4 tool)
• Draw.io (visual editor)
• Mermaid (markdown integration)

2. Integration Tools:

• Documentation generators
• Wiki systems
• Version control systems

Implementation Strategy

1. Start Small

• Week 1: Create Context Diagram
• Week 2: Define Containers
• Week 3: Map Key Components
• Week 4: Link to Code

2. Iterative Refinement

• Get feedback from different stakeholders
• Update based on system changes
• Keep diagrams in sync with code

Alternative Architecture Documentation Approaches

UML (Unified Modeling Language)

Pros:

• Industry standard
• Comprehensive notation
• Tool support

Cons:

• Complex learning curve
• Can be overly detailed
• Less accessible to non-technical users

Arc42

Pros:

• Template-based approach
• Comprehensive documentation
• Well-structured

Cons:

• More documentation-heavy
• Less focus on visual representation
• Can be overwhelming

4+1 View Model

Pros:

• Multiple perspectives
• Scenario-driven
• Well-established

Cons:

• More complex than C4
• Less intuitive hierarchy
• Harder to maintain

Making the Right Choice

When to Use C4

✅ New projects needing clear architecture

✅ Legacy system documentation

✅ Team onboarding

✅ Architecture evolution

When to Consider Alternatives

• When formal UML is required
• For very small projects
• When extensive documentation is needed

Best Practices and Tips

1. Documentation Management

• Keep diagrams with code
• Use version control
• Automate where possible
• Regular reviews and updates

2. Team Adoption

• Start with Context diagrams
• Train team gradually
• Use in code reviews
• Include in documentation

3. Common Pitfalls to Avoid

• Over-complicated diagrams
• Inconsistent notation
• Too much detail too soon
• Outdated documentation

Conclusion

The C4 model provides a structured yet flexible approach to software architecture documentation. Its strength lies in its simplicity and ability to communicate effectively across different audiences while maintaining technical accuracy.

Key Takeaways

1. Start with the big picture (Context)
2. Drill down only when needed
3. Keep diagrams updated
4. Use appropriate detail for your audience

Next Steps

1. Try creating a Context diagram for your current project
2. Experiment with different tools
3. Share and get feedback
4. Iterate and improve

Resources and References

• C4 Model Official Website
• PlantUML
• Structurizr
• Books and articles on software architecture
• Generative AI tools to curate the content

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** Check this real time architecture built in C4 — https://arvind4gl.medium.com/designing-a-qr-based-metro-ticket-booking-system-d1b168795b0f

Please Leave the comments to share the feedback about this article.

Let me know if you want to me take up any other example and create C4 for that in stepwise manner.