API Composition Pattern

1. Introduction

The API Composition Pattern is an architectural style that enables the aggregation of multiple services or APIs into a single cohesive API. This pattern is particularly useful in microservices architectures, where different services can be combined to fulfill specific client requests.

2. Definition

The API Composition Pattern allows applications to compose responses from multiple API calls into a single response. It abstracts the complexity of interacting with multiple services, presenting a unified interface to the clients.

3. How It Works

In API composition, a central API aggregates responses from multiple backend services. The flow typically involves:

1. Client sends a request to the API Gateway.
2. API Gateway forwards the request to the relevant microservices.
3. Microservices respond with their respective data.
4. The API Gateway composes the responses and sends them back to the client.

            graph TD;
                A[Client] -->|Request| B[API Gateway];
                B -->|Call 1| C[Service A];
                B -->|Call 2| D[Service B];
                C -->|Response 1| B;
                D -->|Response 2| B;
                B -->|Composed Response| A;
        

4. Best Practices

• Ensure error handling is robust to manage failures from dependent services.
• Limit the number of services being composed to avoid latency.
• Implement caching mechanisms to enhance performance.
• Use asynchronous calls where possible to improve responsiveness.

5. Code Example

Here’s a simple example of an API composition using Node.js and Express:

const express = require('express');
const axios = require('axios');

const app = express();

app.get('/composed-api', async (req, res) => {
    try {
        const [serviceAResponse, serviceBResponse] = await Promise.all([
            axios.get('http://service-a/api'),
            axios.get('http://service-b/api')
        ]);

        const composedResponse = {
            dataFromServiceA: serviceAResponse.data,
            dataFromServiceB: serviceBResponse.data
        };

        res.json(composedResponse);
    } catch (error) {
        res.status(500).send('Error composing API response');
    }
});

app.listen(3000, () => {
    console.log('API is running on http://localhost:3000');
});
            

6. FAQ