Gateway composition in GraphQL

Introduction

Gateway composition helps combine data from different sources into one simple API. It makes it easy to get all needed info in one place.

You have multiple services each with its own GraphQL API and want to combine them.

You want to hide complexity of many data sources behind one API for your app.

You need to join data from different teams' APIs without changing their code.

You want to improve performance by fetching related data in one request.

You want to add a single entry point for clients to access all backend data.

Syntax

GraphQL

const gateway = new ApolloGateway({
  serviceList: [
    { name: 'users', url: 'http://localhost:4001/graphql' },
    { name: 'products', url: 'http://localhost:4002/graphql' }
  ]
});

const server = new ApolloServer({
  gateway,
  subscriptions: false
});

The serviceList contains all GraphQL services to combine.

Subscriptions are usually disabled in gateway setup.

Examples

This example sets up a gateway combining accounts and reviews services.

GraphQL

const gateway = new ApolloGateway({
  serviceList: [
    { name: 'accounts', url: 'http://localhost:4001/graphql' },
    { name: 'reviews', url: 'http://localhost:4002/graphql' }
  ]
});

This creates the Apollo Server using the gateway and disables subscriptions.

GraphQL

const server = new ApolloServer({
  gateway,
  subscriptions: false
});

Sample Program

This program creates a gateway combining two services: users and products. It starts the server and logs the URL.

GraphQL

import { ApolloServer } from 'apollo-server';
import { ApolloGateway } from '@apollo/gateway';

const gateway = new ApolloGateway({
  serviceList: [
    { name: 'users', url: 'http://localhost:4001/graphql' },
    { name: 'products', url: 'http://localhost:4002/graphql' }
  ]
});

const server = new ApolloServer({
  gateway,
  subscriptions: false
});

server.listen().then(({ url }) => {
  console.log(`🚀 Gateway ready at ${url}`);
});

Important Notes

Each service must have a GraphQL schema that supports federation.

Gateway merges schemas and resolves queries across services automatically.

Make sure services are running before starting the gateway.

Summary

Gateway composition combines multiple GraphQL services into one API.

It simplifies client requests by providing a single endpoint.

Use ApolloGateway with a list of services and disable subscriptions.