Answer.

The Backend for Frontend (BFF) pattern is used when it is necessary to provide different APIs or interfaces for various clients (such as mobile applications, web applications, IoT devices) to optimize their interaction with the backend and hide the internal complexity of microservices. Each type of client gets its own BFF server, which implements a specialized API best suited to the client's needs.

This is convenient when working on large systems — different BFFs allow:

• To aggregate or adapt backend responses to the specific needs of the UI;
• To isolate frontend changes from changes in underlying services;
• To reduce the load on frontend clients by centralizing the optimization and adaptation of data.

Example architecture in Node.js:

// Express for BFF
const express = require('express');
const axios = require('axios');
const app = express();
app.get('/profile', async (req, res) => {
  // Aggregating data from different services
  const [user, settings] = await Promise.all([
    axios.get('http://user-service/api/user'),
    axios.get('http://settings-service/api/settings')
  ]);
  res.json({ name: user.data.name, theme: settings.data.theme });
});
app.listen(3000);

Key features:

• Centralized data processing and validation between the client and microservices
• Improved performance and security management through customization for the client type
• The ability to quickly release improvements for specific platforms without impacting other parts of the system

Tricky questions.

Is BFF just a proxy between clients and microservices?

No. The main difference between BFF and a regular proxy is the presence of business logic and data adaptation. BFF translates and aggregates data, rather than just redirecting requests.

Can one BFF be used for all clients?

No, one of the principles of BFF is to dedicate a BFF for each type of client. Using a single BFF loses the benefits of optimal configuration for different interfaces and device types.

Does BFF increase weak coupling between teams?

It is often answered "yes", but this is not the case: adding BFF often increases coupling, as supporting BFF requires collaboration between frontend and backend teams, which necessitates coordination of changes.