API Composition

Context

You have applied the [[Microservices architecture pattern]] and the [[Database per service]] pattern. As a result, it is no longer straightforward to implement queries that join data from multiple services.

Problem

How to implement queries in a microservice architecture?

Solution

Implement a query by defining an API Composer, which invoking the services that own the data and performs an in-memory join of the results.

Example

An API Gateway often does API composition.

Resulting context

This pattern has the following benefits:

• It a simple way to query data in a microservice architecture

This pattern has the following drawbacks:

• Some queries would result in inefficient, in-memory joins of large datasets.

Related patterns

• The [[Database per Service]] pattern creates the need for this pattern

• The [[CQRS]] pattern is an alternative solution