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.
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.
Last updated
