Why Backend for Frontend (BFF) pattern in Microservices? - Purpose & Use Cases

The Big Idea

What if your app could get exactly what it needs in one simple call, every time?

The Scenario

Imagine building a mobile app and a web app that both need data from many different services. Without a special approach, each app talks directly to all these services, juggling many requests and data formats.

The Problem

This direct approach is slow and confusing. Each app must handle many calls, combine data itself, and deal with different response styles. It leads to duplicated code, more bugs, and poor user experience.

The Solution

The Backend for Frontend (BFF) pattern creates a custom backend for each app type. This backend gathers and shapes data from many services into exactly what the app needs, making the app simpler and faster.

Before vs After

✗ Before

app calls service A, service B, service C separately and merges data on client

✓ After

app calls its BFF once, which fetches and combines data from services A, B, and C

What It Enables

BFF lets each frontend get just the right data in one call, improving speed, reducing complexity, and enabling better user experiences.

Real Life Example

A shopping website and its mobile app use separate BFFs. The website BFF returns detailed product info with images, while the mobile BFF sends a lighter version optimized for small screens and slow networks.

Key Takeaways

Direct calls from frontend to many services cause complexity and slow responses.

BFF creates a tailored backend for each frontend, simplifying data fetching.

This pattern improves performance, reduces bugs, and enhances user experience.

Practice

1. What is the main purpose of the Backend for Frontend (BFF) pattern in microservices architecture?

easy

A. To directly connect frontends to databases without backend logic

B. To replace all microservices with a single monolithic backend

C. To create a backend service tailored specifically for each frontend client

D. To merge all frontend code into one application

Solution

1. Step 1: Understand BFF role

   BFF acts as a specialized backend that serves the needs of a specific frontend, like mobile or web.

2. Step 2: Compare with other options

   Options B, C, and D do not describe BFF but other unrelated or incorrect architectures.

3. Final Answer:

   To create a backend service tailored specifically for each frontend client -> Option C

4. Quick Check:

   BFF = tailored backend for frontend [OK]

Hint: BFF means backend made just for one frontend [OK]

Common Mistakes:

• Thinking BFF replaces microservices
• Confusing BFF with frontend code merging
• Assuming BFF connects frontend directly to database

2. Which of the following is the correct way to describe the BFF pattern's interaction with microservices?

easy

A. BFF aggregates data from multiple microservices for frontend use

B. BFF sends frontend code to microservices

C. BFF replaces microservices with a single service

D. BFF directly modifies microservices' databases

Solution

1. Step 1: Identify BFF's role with microservices

   BFF collects and combines data from various microservices to serve frontend needs efficiently.

2. Step 2: Eliminate incorrect options

   Options A, B, and C describe incorrect or impossible interactions.

3. Final Answer:

   BFF aggregates data from multiple microservices for frontend use -> Option A

4. Quick Check:

   BFF aggregates microservices data [OK]

Hint: BFF collects data from many microservices [OK]

Common Mistakes:

• Assuming BFF changes microservices' databases
• Thinking BFF replaces microservices
• Believing BFF sends frontend code to backend

3. Consider a BFF that calls two microservices: User Service and Order Service. If User Service returns {"name": "Alice"} and Order Service returns {"orders": 3}, what will the BFF likely return to the frontend?

medium

A. {"name": "Alice"}

B. {"orders": 3}

C. {"name": "Alice", "orders": 3}

D. {"user": {"name": "Alice"}, "order": {"orders": 3}}

Solution

1. Step 1: Understand BFF data aggregation

   BFF combines data from multiple microservices into a single response for frontend simplicity.

2. Step 2: Analyze the combined response

   The best practice is to namespace responses to avoid key collisions, resulting in {"user": {"name": "Alice"}, "order": {"orders": 3}}.

3. Final Answer:

   {"user": {"name": "Alice"}, "order": {"orders": 3}} -> Option D

4. Quick Check:

   BFF namespaces microservices data to avoid conflicts [OK]

Hint: BFF namespaces microservices responses [OK]

Common Mistakes:

• Merging keys without namespaces causing conflicts
• Returning only one microservice's data
• Confusing keys or data structure

4. A developer wrote a BFF that calls multiple microservices but the frontend receives slow responses. What is the most likely cause?

medium

A. BFF is making synchronous calls to microservices one after another

B. BFF caches all responses aggressively

C. BFF uses asynchronous calls to microservices

D. BFF compresses responses before sending

Solution

1. Step 1: Identify cause of slow response

   Making synchronous calls one after another causes delays as each waits for the previous to finish.

2. Step 2: Evaluate other options

   Caching and compression usually improve speed; asynchronous calls also improve speed.

3. Final Answer:

   BFF is making synchronous calls to microservices one after another -> Option A

4. Quick Check:

   Synchronous calls cause slow BFF responses [OK]

Hint: Synchronous calls slow down BFF responses [OK]

Common Mistakes:

• Assuming caching slows down responses
• Confusing async with sync calls
• Ignoring network latency impact

5. You are designing a BFF for a mobile app and a web app. The mobile app needs minimal data for fast loading, while the web app needs detailed data. How should you design your BFFs?

hard

A. Use a single BFF that returns all data to both frontends

B. Create separate BFFs for mobile and web, each tailoring data to its frontend

C. Let frontends call microservices directly to get needed data

D. Create one BFF that returns minimal data for both frontends

Solution

1. Step 1: Understand frontend needs

   Mobile requires less data for speed; web requires more detailed data.

2. Step 2: Apply BFF pattern best practice

   Separate BFFs allow tailoring responses to each frontend's needs, improving performance and simplicity.

3. Final Answer:

   Create separate BFFs for mobile and web, each tailoring data to its frontend -> Option B

4. Quick Check:

   Separate BFFs tailor data per frontend [OK]

Hint: Use separate BFFs for different frontend needs [OK]

Common Mistakes:

• Using one BFF for all frontends ignoring needs
• Letting frontends call microservices directly
• Returning minimal data to all frontends