Updated July 2026. Refreshed for current microservices best practices.
What Is CQRS?
Command Query Responsibility Segregation (CQRS) separates write operations (commands) from read operations (queries). In microservices, this means your Order Service might write events to Kafka while a separate read-optimized projection serves search and dashboard queries from Elasticsearch or PostgreSQL read replicas.
Why Use CQRS in Microservices?
- Independent scaling — scale read and write paths separately.
- Optimized models — normalized writes, denormalized reads.
- Clear boundaries — commands enforce business rules; queries stay simple.
- Event-driven sync — Kafka propagates state changes to read models.
Architecture Overview
1. Client sends a command (e.g., CreateOrder) to the write API.
2. Write service validates, persists, and publishes OrderCreated to Kafka.
3. Read projection consumers update a query-optimized store.
4. Client queries the read API for lists, search, and dashboards.
Kafka as the Event Backbone
Apache Kafka 3.x provides durable, ordered event logs. Use topic-per-aggregate (e.g., orders, payments) with partition keys based on aggregate ID to preserve ordering. Consumer groups build read models idempotently.
# Example event schema (JSON)
{
"eventType": "OrderCreated",
"aggregateId": "ord-123",
"timestamp": "2026-07-06T10:00:00Z",
"payload": { "customerId": "cust-1", "total": 99.99 }
}Handling Eventual Consistency
After creating an order, the read model may lag by milliseconds. Return the write result immediately; poll or use WebSockets for read-side updates. Display “Processing…” in UI when stale reads are possible.
When NOT to Use CQRS
Skip CQRS for simple CRUD apps with uniform read/write patterns. Adopt it when read and write loads differ significantly, or when combined with event sourcing for audit trails.
Related: Event Sourcing Explained · Outbox Pattern · Microservices Introduction
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Kindson Munonye is a software engineer and technical author specializing in microservices, CQRS, event sourcing, and distributed systems. He publishes free step-by-step tutorials and live classes on Alkademy.