Don’t worry, nothing will blow up. C4 Model isn’t an explosive material, it’s a way to visualize your system’s architecture. It was created by Simon Brown, a software architect who wanted a more practical approach to documenting systems.
The C4 technique is heavily inspired by Unified Modeling Language (UML), a general-purpose modeling language for software engineering. The idea behind UML was to create a standard way to visually represent any computer system, like blueprints for software. Did it succeed? Well, have you ever used UML in your professional career? If so, I hope it helped. If not, you might find something more practical in C4 Model.
What Exactly Is the C4 Model?
The C4 model is an abstraction technique that helps architects and development teams create a shared understanding of a software system’s architecture through visual diagrams. It captures key structural elements and their relationships at different levels of abstraction. The model consists of a hierarchical set of diagrams, each focusing on a specific level of detail.
Levels of Abstraction
Simon Brown designed C4 with a Google Maps-style navigation approach. You start with a high-level overview and zoom in to see more details.
Level 1: Context
This is the most zoomed-out view. The context diagram provides a high-level overview of the system, showing how it interacts with external actors and other systems. It illustrates system boundaries, users, external services, and major components.
Level 2: Container
Container diagrams zoom in on the system’s internal structure, highlighting key containers that make up the system. A container represents a runtime environment that hosts a set of related components or services. To see which containers exist within a given context, zoom in one level.
Level 3: Component
Component diagrams break down individual containers from the previous level into their core components. Components represent major building blocks of the system, encapsulating cohesive functionality. These aren’t separate deployments, think of web controllers, application services, or domain logic within your project.
Level 4: Code
At the lowest level, code diagrams provide insight into the internal structure of individual components. These can document implementation details, dependencies, and internal interactions. However, mapping out your project at this level can lead to bloated diagrams filled with generic boilerplate. Use this level sparingly, focusing only on critical algorithms or formulas that need clarification.
Monolith vs. Microservices: How Visualization Differs
In a monolithic system, the C4 model typically results in:
- A single container representing the entire application.
- Fewer external dependencies since most logic resides in one place.
- Simpler component diagrams, showing layers within the monolith (controllers, services, repositories, etc.).
For microservices, the visualization changes significantly:
- Multiple containers, each representing a separate microservice.
- Complex interactions between services, often requiring additional diagrams to show API calls, event flows, or message queues.
- More external dependencies, including databases, caches, and third-party integrations.
The key takeaway? In a monolith, the focus is on internal structure, while in microservices, it’s about inter-service communication and how everything fits together.
Benefits of the C4 Model
Scalability
The hierarchical structure of the C4 model makes it easy to scale diagrams to different levels of detail. From high-level context to detailed code diagrams, the model adapts to different stakeholders’ needs.
Improved Communication
Visualizing the system architecture makes it easier for team members, stakeholders, and external parties to understand the system. It reduces ambiguity, promotes collaboration, and helps during design discussions.
Lightweight Documentation
C4 diagrams are more accessible and easier to grasp than traditional text-based documentation. They provide a structured way to document software architecture without unnecessary complexity.
Better Decision-Making
By mapping out dependencies and relationships, C4 diagrams help architects analyze risks, evaluate trade-offs, and make informed design choices. They also assist developers during code reviews and refactoring by providing context around the codebase.
Structurizr: Keeping Your Architecture as Code
Structurizr is a tool that lets you define C4 diagrams using a Domain-Specific Language (DSL). This means you can store your architecture diagrams as code, version-control them, and automatically update them as your architecture evolves. Structurizr helps ensure diagrams stay up to date, allowing architects and teams to review changes before merging updates into the main branch.