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🧩 Backends-for-Frontends (BFF) — Quick Guide

Backends-for-Frontends (BFF) is a design pattern where you create a dedicated backend for each frontend (e.g., web, mobile, IoT). It helps tailor API responses, reduce over-fetching, and decouple frontend and backend teams.

🔧 What Is BFF?

A BFF is a service layer that sits between frontend applications and backend APIs or services. Each frontend (like Web, iOS, Android) can have its own BFF that caters specifically to its needs.

🎯 Why Use BFF?

✅ Tailor APIs to frontend needs (no over-fetching/under-fetching).
✅ Encapsulate frontend-specific logic (formatting, transformations).
✅ Enable faster frontend iteration without breaking backend services.
✅ Manage authentication, rate limits, caching, aggregation.
✅ Help enforce separation of concerns between frontend and backend.

🧱 Common Patterns

1. Device-Specific BFFs

Create separate BFFs for Web, Mobile, and others.

bff-web.example.com
bff-mobile.example.com

2. Unified Gateway + BFF

Use an API Gateway for routing + lightweight BFFs for logic.

3. Micro-BFFs

Frontend teams own and deploy their own micro-BFFs per domain or module.

4. Monolith BFF

One BFF service handles all frontend types. Useful for small teams.

⚙️ Responsibilities of a BFF

Aggregate responses from multiple microservices
Transform data formats for frontend needs
Authenticate users and manage tokens
Handle rate limiting or feature toggles
Perform caching or batching
Apply localization or feature experiments

📦 Example Use Case

GET /dashboard (from Mobile BFF)
→ Aggregates:
   - User Profile Service
   - Notifications Service
   - Billing Service
→ Returns mobile-optimized response

🛑 When Not to Use BFF

When all clients can use the same generic backend.
If your team is too small to maintain multiple backend layers.
When API Gateway alone can do basic transformations.

✅ Best Practices

Co-locate frontend and BFF teams for tight feedback loops.
Keep BFF stateless and scalable.
Use versioning to avoid breaking clients.
Limit business logic in BFF — push that to backend services.

🏁 Summary

Benefit	Description
Tailored APIs	Custom responses per device
Frontend Agility	Changes in BFF don’t require backend changes
Simplified Frontend	Aggregates and flattens complex data
Decoupled Logic	Keeps UI logic out of core services

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