Q: You want to migrate a monolithic backend to microservices. The frontend team complains that they will now have to make 15 separate API calls to 15 different microservices just to load the user profile page. How do you solve this architectural bottleneck?

Forcing the client browser or mobile app to manage complex network orchestration, aggregations, and individual microservice latencies creates a horrible user experience. The solution is to insert a Backend-For-Frontend (BFF) or an Aggregation API layer (often implemented via GraphQL or an API Gateway). The frontend makes exactly one API call to the BFF. The BFF, living inside the highly-connected server data center, rapidly fans out the 15 internal requests to the microservices, aggregates the responses into a single, clean JSON payload, and sends that consolidated object back to the client device over the slow internet connection.