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Introduction to C4 Diagrams

C4 Diagrams are a set of hierarchical diagrams that provide a clear and structured way to visualize the architecture of a software system. Developed by Simon Brown, C4 focuses on showing different levels of detail through four distinct diagrams: Context, Container, Component, and Code. The C4 model is highly beneficial for communicating both the broad structure and detailed internals of a system.

The Four Levels of C4 Diagrams:​

  1. Context Diagram (Level 1):
    The highest-level diagram that shows the system in relation to external users (actors) and other systems it interacts with. It helps identify the boundaries of the system and the key external dependencies, without going into implementation details. This diagram is ideal for introducing a system to stakeholders.

  2. Container Diagram (Level 2):
    This diagram provides a breakdown of the internal structure of the system, focusing on its containers (such as web servers, databases, microservices). Each container represents a deployable unit, and the diagram shows how these containers communicate with each other. It’s particularly useful for showing the high-level technical architecture.

  3. Component Diagram (Level 3):
    A more detailed view of the internal workings of a specific container, this diagram illustrates the components that make up the container. Components are individual modules or services, and the diagram shows how they interact to fulfill the container’s responsibilities. This level of detail is beneficial for developers and architects to understand specific areas of the system.

  4. Code Diagram (Level 4):
    The lowest level, this diagram shows the structure of the source code itself (e.g., classes, interfaces). Although this diagram is rarely used due to the potential for detail overload, it can be helpful for very detailed technical discussions. In most cases, modern tools like IDEs and code editors provide this view.

Benefits of C4 Diagrams:​

  • Clarity at Multiple Levels: By breaking down the system into four levels, each diagram presents information at the right level of detail for different stakeholders (non-technical stakeholders, developers, operations teams, etc.).
  • Consistency: All four diagrams follow a consistent structure, making it easier to understand the system holistically as you dive into each level.
  • Effective Communication: C4 Diagrams help bridge the communication gap between technical teams and business stakeholders, offering both a high-level overview and a deep-dive into system components.

How to Use C4 Diagrams:​

  • Start with the Context Diagram to establish the system’s boundaries and external relationships.
  • Then use the Container Diagram to understand the overall structure and responsibilities of the system's main components.
  • For a deep dive into a particular part of the system, use a Component Diagram to visualize the inner workings of individual containers.
  • Optionally, if further detail is needed, create a Code Diagram for exploring the implementation of specific components.

C4 Diagrams are an essential tool in modern software architecture documentation, providing a standardized way to describe systems that scales from a broad overview to in-depth technical details.