Senior LevelREST APIs & Web Services
How do CQRS and Event Sourcing transform API data read and write models?
❓ Interview Prompt: Explain Command Query Responsibility Segregation (CQRS), Event Sourcing, write-optimized Command API vs read-optimized Query API (Elasticsearch/Redis).
Separating write operations from read operations in high-scale REST architectures using CQRS and Event Sourcing:
CQRS Architecture:
1
Command API ('POST /api/v1/orders'): Accepts write commands, appends events to an append-only Event Store ('OrderCreatedEvent'), and emits events to Kafka.
2
Event Handlers: Asynchronously project events into read-optimized databases (Elasticsearch, Redis).
3
Query API ('GET /api/v1/orders/search'): Executes ultra-fast search queries against Elasticsearch without touching the write database!
Code Implementation Example
typescript
// CQRS Command API Handler (Appends event to Event Store)
export async function handleCreateOrderCommand(command: CreateOrderCommand) {
const event = new OrderCreatedEvent(command.orderId, command.amount);
await eventStore.append('orders', command.orderId, event);
await kafka.publish('order-events', event);
return { status: 'ACCEPTED', orderId: command.orderId };
}💡CQRS Command API handler appending events to Event Store.
🎯 Interview Key Takeaway
Use CQRS to decouple write operations from read queries, projecting events into read-optimized databases for ultra-fast query execution.
#CQRS#Event Sourcing#Architecture#Senior
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