Q16: Tell me something about CQRS?
Q17: Do we have two different databases in CQRS?
Q18: Techniques to keep two database in Sync?
Q19: Define Database per Microservice Architecture Design pattern? [Microservice Architecture Design patterns -- Database per Microservice, Event Sourcing, CQRS, Saga, BFF, API Gateway, Strangler, Circuit Breaker, Externalized Configuration, Consumer-Driven Contract Tracing]
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Q16: Tell me something about CQRS?
Answer:
CQRS (Command Query Responsibility Segregation) is a powerful architectural pattern often used in microservices to separate the responsibilities of reading and writing data
Benefits:
>> This separation allows each side to be optimized independently for performance, scalability, and complexity.
CQRS splits the application into two distinct parts:
Command Side (Write Model): Handles operations that change data (Create, Update, Delete).
Query Side (Read Model): Handles operations that retrieve data (Read).
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Q17: Do we have two different databases in CQRS?
Answer:
In CQRS, it's common but not mandatory to use two separate databases for the read and write sides.
Benefits of using Two databases:
1. Independent Scaling : We can scale READ DB horizontally to handle high query loads.
2. Technology Flexibility: You might use a relational database (e.g., PostgreSQL) for writes. And a NoSQL database (e.g., MongoDB, Elasticsearch) for reads.
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Q18: Techniques to keep two database in Sync?
Answer:
Techniques
1. Event-Driven Synchronization (Most Common)
- How it works: After a write operation, the system emits a domain event (e.g., OrderCreated, CustomerUpdated).
- These events are published to a message broker (like Kafka, RabbitMQ, or Azure Service Bus).
- A consumer service listens to these events and updates the read database (e.g., MongoDB).
- This enables eventual consistency (With little latency).
2. Dual Writes (Not Recommended)#
The application writes to both databases in the same transaction or sequentially.
⚠️ Cons:
Risk of inconsistency if one write fails.
Hard to manage rollback and error handling.
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Q19: Define Database per Microservice Architecture Design pattern?
Answer:
Each Microservice has its own dedicated Database and un related microservice can NOT access db of other domain directly.
Advantages:
1. Understanding of Project and related DB is easy as it has limited tables and data.
2. Scaling of DB is easy as required.
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