The C4 model, or Context, Container, Component, and Code model, is a framework for visualizing the architecture of software systems. It was developed by Simon Brown and is widely used in the field of cloud computing. This model provides a static view of a system and is particularly useful for communicating software architecture to different stakeholders, including developers, project managers, and clients.
The C4 model is a hierarchical way to think about the static structures of a software system in terms of containers, components, and classes or code. It's a way to create maps of your code, at various levels of detail, in the same way you would use Google Maps to zoom in and out of an area. The C4 model considers the static structures of a system, rather than its dynamic behaviour.
Definition of C4 Model
The C4 model is a framework for visualizing the architecture of a software system. It is composed of four levels: Context, Container, Component, and Code. Each level provides a different level of detail and is intended for a different audience. The C4 model is a way to create maps of your code, at various levels of detail, in the same way you would use Google Maps to zoom in and out of an area.
The Context level shows the high-level view of a system, including its boundaries and interactions with users and external systems. The Container level shows the internal structure of the system, including the major software or hardware elements that host the system. The Component level shows the internal structure of a container, including the major software modules and their interactions. The Code level shows the internal structure of a component, including the classes or interfaces and their interactions.
Context Level
The Context level of the C4 model provides a high-level view of a system. It shows the system as a single box and includes its interactions with users and external systems. This level is intended for non-technical stakeholders who need to understand the system's purpose and interactions but do not need to understand its internal structure.
The Context level is often represented as a diagram, with the system shown as a single box in the center. The interactions with users and external systems are shown as arrows pointing to or from the box. These interactions can be labeled to indicate the nature of the interaction, such as "sends data to" or "receives data from".
Container Level
The Container level of the C4 model provides a more detailed view of a system. It shows the major software or hardware elements that host the system, such as web servers, databases, mobile apps, and desktop applications. This level is intended for software architects and developers who need to understand the high-level technology decisions and the distribution of responsibilities among the containers.
The Container level is often represented as a diagram, with each container shown as a box within the system box. The interactions between containers are shown as arrows pointing between the boxes. These interactions can be labeled to indicate the nature of the interaction, such as "reads from" or "writes to".
History of C4 Model
The C4 model was developed by Simon Brown, a software architect and author, in response to the lack of a standard way to describe the architecture of a software system. Brown found that traditional methods of visualizing software architecture, such as UML diagrams, were often too detailed and complex for non-technical stakeholders to understand. At the same time, they were too high-level and abstract for developers to use as a guide for implementation.
Brown introduced the C4 model in his book "Software Architecture for Developers", which was published in 2015. The model quickly gained popularity among software architects and developers for its simplicity and effectiveness in communicating software architecture. Today, the C4 model is widely used in the field of cloud computing and is supported by several software tools.
Simon Brown and the Development of C4 Model
Simon Brown is a software architect and author who has worked in the software industry since the late 1990s. He has worked on a variety of projects, from small startups to large corporations, and has a deep understanding of the challenges and complexities of software architecture.
Brown developed the C4 model as a way to simplify the communication of software architecture. He saw that traditional methods of visualizing software architecture were often too complex for non-technical stakeholders to understand and too abstract for developers to use as a guide for implementation. The C4 model was his solution to these problems.
Adoption and Use of C4 Model
The C4 model has been widely adopted in the software industry, particularly in the field of cloud computing. It is used by software architects and developers to visualize the architecture of a system, communicate design decisions, and guide the implementation of a system.
The C4 model is supported by several software tools, including Structurizr, a cloud-based software architecture tool developed by Simon Brown. Structurizr provides a web-based interface for creating and viewing C4 diagrams, and supports the export of diagrams to various formats, including PDF and PNG.
Use Cases of C4 Model
The C4 model is used in a variety of scenarios in the field of cloud computing. It is used to visualize the architecture of a system, communicate design decisions, guide the implementation of a system, and document the architecture of a system for future reference.
One common use case of the C4 model is during the design phase of a project, when the architecture of a system is being defined. The C4 model can be used to create a visual representation of the proposed architecture, which can be shared with stakeholders for feedback and approval. The C4 model can also be used to guide the implementation of the system, by providing a clear and detailed map of the system's structure.
Design Phase
During the design phase of a project, the C4 model can be used to create a visual representation of the proposed architecture. This can be particularly useful when the architecture is complex and involves multiple containers and components.
The C4 model can help to clarify the architecture and make it easier for stakeholders to understand. It can also help to identify potential issues or gaps in the architecture, which can be addressed before the implementation phase begins.
Implementation Phase
During the implementation phase of a project, the C4 model can be used to guide the development of the system. The C4 diagrams can serve as a map of the system, showing the structure of the containers and components and the interactions between them.
The C4 model can also be used to document the architecture of the system for future reference. This can be particularly useful for large systems, where the architecture can be complex and difficult to understand without a visual guide.
Specific Examples of C4 Model
There are many examples of the C4 model being used in the field of cloud computing. These examples demonstrate the versatility and effectiveness of the C4 model in visualizing the architecture of a system, communicating design decisions, and guiding the implementation of a system.
One example is the architecture of a cloud-based web application. The Context level of the C4 model shows the interactions between the web application, its users, and external systems such as databases and APIs. The Container level shows the internal structure of the web application, including the web server, application server, and database. The Component level shows the internal structure of the application server, including the major software modules and their interactions. The Code level shows the internal structure of a component, including the classes or interfaces and their interactions.
Cloud-Based Web Application
A cloud-based web application is a common use case for the C4 model. The Context level of the C4 model shows the interactions between the web application, its users, and external systems such as databases and APIs. This level provides a high-level view of the system and is intended for non-technical stakeholders.
The Container level of the C4 model shows the internal structure of the web application, including the web server, application server, and database. This level provides a more detailed view of the system and is intended for software architects and developers. The Component level shows the internal structure of the application server, including the major software modules and their interactions. The Code level shows the internal structure of a component, including the classes or interfaces and their interactions.
Microservices Architecture
A microservices architecture is another common use case for the C4 model. The Context level of the C4 model shows the interactions between the microservices, their users, and external systems. This level provides a high-level view of the system and is intended for non-technical stakeholders.
The Container level of the C4 model shows the internal structure of the microservices, including the individual services and their interactions. This level provides a more detailed view of the system and is intended for software architects and developers. The Component level shows the internal structure of a service, including the major software modules and their interactions. The Code level shows the internal structure of a component, including the classes or interfaces and their interactions.
