API Composition

Definitions

1. A pattern where a service (or API gateway) queries multiple microservices and combines the results into a single response. Replaces cross-service database joins that are impossible in a microservice architecture. The composer handles fan-out, error handling, and response assembly. Simple alternative to CQRS for read-heavy queries spanning multiple services.

   In plain English: Combining data from multiple microservices into a single API response, since you can't join across separate databases.

   Example: "The product detail page composer calls the catalog, pricing, inventory, and reviews services in parallel and merges the responses."

Related Terms

• Webhook vs. Polling
• Event-Driven Architecture
• Service Mesh
• Circuit Breaker
• Idempotency Key
• Contract Testing
• API Gateway Pattern
• Backend for Frontend