CQRS stands for Command Query Responsibility Segregation. This pattern divides an application into two parts: the Command side and the Query side. The Command side handles tasks that modify data (create, update, delete), while the Query side manages data retrieval (read). This separation offers numerous advantages, particularly in microservices architecture.
Separation of Concerns: By separating read and write operations, CQRS allows for the optimization of each operation independently. This separation means that read and write databases can be scaled according to their specific load. Load Balancing: In systems with different read and write load, CQRS allows for balancing these loads more effectively. For instance, a system with heavy read operations can have more resources dedicated to the query side.
Technology Agnostic: Each side (Command and Query) can use technologies best suited for their purpose. For example, a document-based NoSQL database might be ideal for reads, while a relational database could be preferred for writes. Simplified Complex Systems: CQRS is beneficial in systems with complex business logic, as it allows developers to focus on either command or query responsibilities, reducing the cognitive load.
Command Side: When a command is issued (like creating or modifying data), it is processed by the command model. The resulting events (e.g., data updated, item created) are published to a Kafka topic. Event Processing: Apache Kafka acts as the event backbone. It ensures that events are durably stored and facilitates the asynchronous communication between microservices. Query Side: The query microservices subscribe to relevant Kafka topics. When an event is consumed, it updates the query database according to the incoming event type (UPDATE, CREATE, DELETE).
CQRS pattern provides a powerful architecture and separation of concerns for building scalable, maintainable, and flexible applications; capable of tailoring different parts for different workloads. It addresses the challenges of handling high-throughput, distributed systems, and complex domain models.