advanced

BFF pattern

Use a backend-for-frontend to shape APIs around client workflows while controlling duplication, caching, auth, and ownership boundaries.

Backend-for-Frontend (BFF) tailors APIs to specific client workflows—mobile, web, partner—aggregating downstream services, shaping payloads, and handling client-specific auth or caching. It reduces over-fetching and chatty clients but risks duplication if every screen gets its own BFF endpoint without governance.

On interviews: justify BFF versus generic API gateway or GraphQL. Explain ownership—frontend team, platform team, or shared—and caching boundaries.

Common pitfalls: BFF becoming a second monolith; business rules duplicated from core services; no contract tests between BFF and clients.

The trade-off is flexibility versus complexity—know when the simpler path is enough.

Checklist:

BFF optimized for one client experience.
Domain rules stay in core services.
Aggregation with timeouts and partial failure strategy.
Versioned contracts tested with consumer fixtures.