Design Modular & Loosely Coupled Systems

This standard outlines fundamental principles for digital engineering, focusing on the creation of robust, adaptable, and maintainable systems. It emphasises a shift from monolithic architectures to modular, loosely coupled designs that promote agility and innovation.

1. Design Modular & Loosely Coupled Systems:

Software should be architected as a collection of independent, reusable components with clear boundaries. This approach enhances maintainability, scalability, and reduces the impact of changes.

  • 1.1 Domain-Driven Design (DDD):
    • Employ DDD to model complex business domains, defining bounded contexts and ubiquitous languages.
    • Identify core domains, supporting subdomains, and generic subdomains to prioritise development effort.
    • Utilise tactical DDD patterns (Entities, Value Objects, Aggregates, Services, Repositories) for effective implementation.
    • 1.1.1 Bounded Contexts: Explicitly define the boundaries within which a particular domain model applies. Ensure clear communication and integration between bounded contexts.
    • 1.1.2 Ubiquitous Language: Establish a shared vocabulary between domain experts and developers to ensure accurate representation of the domain in the code.
  • 1.2 Loose Coupling through Contracts:
    • Minimise direct dependencies between components by defining well-defined contracts (interfaces, APIs).
    • Use asynchronous communication patterns (message queues, event buses) for decoupled interactions where appropriate.
    • Employ dependency injection to manage component dependencies and promote testability.
    • 1.2.1 API-First Design: Prioritise API design, ensuring clear documentation and versioning for seamless integration.
    • 1.2.2 Event-Driven Architectures: Utilise event sourcing and CQRS patterns when applicable, to improve scalability and responsiveness.
  • 1.3 Single Responsibility Principle (SRP):
    • Ensure each component has one, and only one, reason to change.
    • Promote separation of concerns to improve code clarity and reduce the risk of unintended side effects.
    • 1.3.1 Cohesion: Maximise the relatedness of elements within a component.
    • 1.3.2 Coupling: Minimise the dependencies between components.

2. Embrace Automation and Continuous Delivery:

Automation is crucial for achieving rapid and reliable software delivery.

  • 2.1 Infrastructure as Code (IaC):
    • Manage infrastructure using code (e.g., Terraform, CloudFormation) to ensure consistency and repeatability.
    • Automate infrastructure provisioning and configuration to reduce manual errors.
  • 2.2 Continuous Integration/Continuous Delivery (CI/CD):
    • Implement automated build, test, and deployment pipelines.
    • Utilise version control (Git) for code management and collaboration.
    • Employ automated testing (unit, integration, end-to-end) to ensure code quality.
    • 2.2.1 Trunk Based Development: Promote small, frequent merges into a main branch to reduce integration conflicts.
    • 2.2.2 Feature Flags: Use feature flags to enable gradual rollouts and controlled experimentation.
  • 2.3 Automated Testing Strategies:
    • Implement layered testing, including unit tests, integration tests, and end-to-end tests.
    • Automate performance and security testing.
    • Utilize test driven development (TDD) where applicable.

3. Prioritize Observability and Monitoring:

Gain deep insights into system behaviour to ensure reliability and performance.

  • 3.1 Logging and Tracing:
    • Implement structured logging to capture relevant system events.
    • Utilise distributed tracing to track requests across multiple services.
  • 3.2 Monitoring and Alerting:
    • Monitor key performance indicators (KPIs) and set up alerts for critical events.
    • Use dashboards and visualisation tools to gain real-time insights into system health.
  • 3.3 Incident Management:
    • Develop a clear incident response process.
    • Conduct post-incident reviews to identify root causes and improve system resilience.

4. Focus on Security by Design:

Integrate security considerations into every stage of the development lifecycle.

  • 4.1 Secure Coding Practices:
    • Follow secure coding guidelines (e.g., OWASP Top 10).
    • Perform regular code reviews and security audits.
  • 4.2 Authentication and Authorization:
    • Implement robust authentication and authorization mechanisms.
    • Follow the principle of least privilege.
  • 4.3 Data Protection:
    • Encrypt sensitive data at rest and in transit.
    • Implement data masking and anonymisation techniques.

5. Embrace Evolutionary Architecture:

Design systems that can evolve and adapt to changing business needs.

  • 5.1 Microservices Architecture (Where Applicable):
    • Break down monolithic applications into smaller, independent services.
    • Promote decentralised governance and technology choices.
  • 5.2 API Evolution:
    • Design APIs with versioning in mind, and ensure backwards compatibility.
    • Document API changes, and provide clear migration paths.
  • 5.3 Technology Agility:
    • Evaluate and adopt new technologies and practices that align with business goals.
    • Promote continuous learning and knowledge sharing within the team.

This standard is a living document and should be adapted to the specific needs of each project and organisation. By adhering to these principles, we can build digital systems that are not only functional but also resilient, scalable, and adaptable to the ever-changing digital landscape.