Component to Component

Asynchronous Messaging and CQRS

In a RECQ architecture, components communicate with each other indirectly through asynchronous message exchange facilitated by the Message Gateway. This communication adheres to the Command Query Responsibility Segregation (CQRS) pattern, enforcing a clear separation between commands that modify the system state and queries that retrieve data without causing state changes.

Message Types and Protocols:

• Commands:

  • Commands typically follow a request/reply pattern:

    • The component sends a command message to the Message Gateway, specifying the desired action.

    • The Message Gateway routes the command to the appropriate Command Service.

    • The Command Service processes the command and performs the requested action.

    • The Command Service sends a response message back through the Message Gateway, indicating the success or failure of the operation.

    • The Message Gateway delivers the response message to the originating component.

  • Since the CQRS pattern is enforced, the response message for a command typically only includes confirmation of success or failure (e.g., boolean flag or error code) and not the updated data itself.

• Queries:

  • Queries typically follow a request/reply pattern:

    • The component sends a query message to the Message Gateway, specifying the requested data.

    • The Message Gateway routes the query to the appropriate Query Service.

    • The Query Service retrieves the data from the system state or relevant data store.

    • The Query Service sends a response message back through the Message Gateway, containing the requested data (the Views).

    • The Message Gateway delivers the response message containing the data (Views) to the originating component.

Component to Component Communication

Benefits of Asynchronous Messaging and CQRS:

• Improved Scalability and Performance: Asynchronous message exchange allows components to send requests without waiting for immediate responses. This decouples components and enables independent scaling based on their workload.

• Enhanced Maintainability: Separating commands and queries simplifies the logic within each component and promotes code clarity.

• Optimized Event Sourcing: Separating commands from queries, updating the system state with commands and retrieving data through queries promotes a cleaner separation of concerns for event sourcing.

Considerations:

• Increased Complexity: Asynchronous messaging and CQRS introduce additional complexity compared to simpler synchronous communication patterns.

• Potential for Data Inconsistency: In rare cases, if events haven't been processed by the System State Store when a query is sent, the retrieved data might not reflect the latest state. Techniques like eventual consistency or materialized views can be used to mitigate this.

Conclusion:

Leveraging asynchronous messaging with the mandatory Message Gateway and adhering to the CQRS pattern provides a robust and scalable approach for component-to-component communication in a RECQ architecture. This approach promotes loose coupling, improves maintainability, and optimizes event sourcing for event-driven microservices.