C4+1 — The Services Layer

David R Oliver
4 min readMay 29, 2024

Adding an extra layer to the C4 Model helps solve the age-old problem of where you put the Services.

The C4 Model with an extra Services layer.

Introduction

Having used the C4 model (Context, Containers, Components, and Code) for many years in various projects, I’ve noticed its strengths and areas for potential enhancement.

A recurring challenge in C4 is the ambiguity often encountered in differentiating between Containers and Components. This ambiguity can lead to confusion, particularly in complex Architectures using Microservices or, more recently, Data Mesh patterns.

Proposed Solution

To address this issue, I’ve used an additional layer called Services, which is placed between the Container and Component layers of the C4 model. This Services layer aims to provide a clear demarcation, explicitly defining the roles and responsibilities that might overlap between Containers and Components. For instance, in a web application architecture, the Services layer could be responsible for distinct backend functionalities, such as API management and data processing, which are not explicitly covered by either Containers or Components.

Use Cases

Introducing a Services layer in the C4 model can be particularly beneficial in various scenarios:

  • Large-Scale Enterprise Applications: A Services layer can help organise and segregate functionalities like security, data processing, and communication services in complex applications with multiple interacting components, such as those found in large enterprises.
  • Microservices Architectures: The Services layer can clearly define each Microservice’s services for systems designed around microservices, facilitating better modularity and scalability.
  • API-Centric Systems: In systems where external APIs play a crucial role, the Services layer can manage these integrations, distinguishing them from core business logic contained in other layers.
  • Cloud-Based Solutions: For cloud-native applications, the Services layer can handle interactions with cloud services such as storage, computing, and database services, thereby separating cloud-specific concerns from the rest of the application.
  • E-Commerce Platforms: E-commerce applications can benefit from a Services layer by managing services related to payment processing, inventory management, and customer interactions separately from the core application logic.

Pros and Cons

To be honest, there are Pros and Cons of this approach so lets examine them.

Pros

  • Enhanced Clarity and Definition: Adding a Services layer can provide clearer distinctions between Containers and Components, which helps better understand and define each layer’s responsibilities and roles.
  • Improved Organisation: This layer can bring more structure to the architecture, making organising and managing complex systems easier.
  • Facilitates Modularity: By clearly defining Services, it becomes easier to modularise functionalities, leading to better system maintainability and scalability.
  • Enhanced Communication: A well-defined architecture with distinct layers can facilitate the communication ofthe design to both technical and non-technical stakeholders.
  • Streamlines Development Process: Clear segregation can streamline the development process, as developers better understand where to implement specific functionalities.

Cons:

  • Increased Complexity: Introducing an additional layer can make the architecture more complex, especially for smaller or less complex systems where this level of detail might be unnecessary.
  • Potential Overhead: The added layer could introduce more overhead regarding design, documentation, and maintenance.
  • Learning Curve: For teams already familiar with the standard C4 model, adapting to this new layer might require many different types of adjustments, such as changes in standards and training.
  • Possible Redundancy: There’s a risk of redundancy if the roles of the Services layer overlap significantly with existing Containers or Components.
  • Implementation Challenges: Ensuring the Services layer is correctly and consistently implemented across different projects can be challenging, especially in larger organisations; it may take time to sync up.

Mapping C4 to TOGAF Metamodel

The TOGAF Metamodel provides a structured approach to architecture. It serves as a valuable starting point for organisations looking to leverage the benefits of a structured Metamodel, particularly in understanding and managing the relationships between different architectural components.

However, it’s important to recognise that the TOGAF Metamodel is not a one-size-fits-all solution. Tailoring the Metamodel to fit an organisation’s specific needs and context is often necessary. Customisation makes the Metamodel more relevant and valuable to the organisation, enhancing its effectiveness and the likelihood of its adoption.

Integration with methodologies like the C4 model (Context, Containers, Components, and Code) becomes beneficial. The C4 model complements the TOGAF Metamodel by providing a clear and structured approach to software architecture, which helps manage the level of detail without overcomplicating the architecture.

The following table shows what C4 level the elements of the Metamodel reside in:

A ‘Data Entity’ is in the Services Column because it is helpful to have this here if we use a data mesh or data fabric.

Conclusion

Introducing a Services layer in the C4 model can clarify and better organise complex systems, but it also introduces additional complexity and potential overhead. The decision to adopt this approach should be carefully considered based on the project or organisation’s specific needs and context.

Recommendations

  • Assessment of Complexity: Evaluate the complexity of your system to determine if the additional Services layer is necessary.
  • Clear Documentation: Ensure thorough documentation to mitigate potential overhead and redundancy.
  • Training: Provide adequate training for teams to adapt to the enhanced model.
  • Pilot Implementation: Before wide-scale adoption, consider piloting the new model in a smaller project to understand its benefits and challenges.

By weighing the pros and cons and considering their projects’ specific needs, organisations can make an informed decision about incorporating the Services layer into their architectural practices.

Any thoughts and feedback are all most welcome. Thank you for your time and attention.

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David R Oliver

Solution Architecture | Knowledge Management | Writer | Mentor | Cats