CQRS Architecture Diagram Template

What this template is for

A CQRS (Command Query Responsibility Segregation) architecture diagram shows how a system separates writes from reads using two distinct models connected by events. This template lays out the canonical CQRS shape: a command side that handles writes through command handlers and a write model (often event-sourced), an event store, an event bus that publishes events, a projector that listens and updates the read model, and a query side that serves reads from the optimized read model. Use it to design a CQRS service, explain the eventual consistency between write and read, or document why a single API endpoint splits into two backend paths.

When to use this template

• Design a CQRS service before writing the first command handler.
• Explain why writes go through one path and reads through another.
• Document the projection step that builds the read model from events.
• Plan the eventual-consistency boundary between command and query sides.
• Trace a stale read: did the projector lag, fail, or fall behind?
• Compare CQRS against a single-model (CRUD) approach to justify the complexity.

How to use it

1. 1Start with the client and API gateway routing commands and queries.
2. 2Draw the command side: command handler, write model, event store.
3. 3Draw the query side: query handler, read model, projector.
4. 4Add an event bus between them that publishes events from the store.
5. 5Connect the projector to the bus and to the read model.
6. 6Label the consistency boundary — eventual between write and read.

Quick example