GraphQL Federation

1. Introduction

GraphQL Federation is a powerful architecture for composing multiple GraphQL services into one data graph. It enables teams to build and evolve their GraphQL services independently while providing a unified API for clients.

Note: Federation allows for modularity in GraphQL services, making it easier to scale and maintain.

2. Key Concepts

Subgraph: A single GraphQL service that contributes to the overall schema.
Gateway: A combined entry point for clients to access the federated GraphQL services.
Entity: A type that can be extended by multiple subgraphs.

3. Step-by-Step Implementation

3.1 Setting Up a Subgraph

To create a subgraph, you need to define your schema and use the @key directive to mark entities.


const { ApolloServer } = require('apollo-server');

const typeDefs = `
  type User @key(fields: "id") {
    id: ID!
    name: String
  }
`;

const resolvers = {
  User: {
    __resolveReference(user) {
      return users.find(u => u.id === user.id);
    },
  },
};

const server = new ApolloServer({ typeDefs, resolvers });
server.listen().then(({ url }) => {
  console.log(\`Subgraph ready at \${url}\`);
});

3.2 Setting Up the Gateway

Once your subgraphs are set up, create a gateway to combine them:


const { ApolloGateway } = require('@apollo/gateway');
const { ApolloServer } = require('apollo-server');

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}\`);
});

4. Best Practices

Use @key directive for defining entities.
Keep subgraphs focused on specific domains.
Regularly update schema and gateway configurations to reflect changes.
Implement versioning to manage breaking changes effectively.

5. FAQ

What is GraphQL Federation?

GraphQL Federation is a method for composing multiple GraphQL services into a single data graph, enabling modular development.

How does Federation improve scalability?

It allows teams to build and maintain their GraphQL services independently, reducing interdependencies and easing scaling efforts.

Can I use Federation with existing GraphQL services?

Yes, existing GraphQL services can be integrated into a federated architecture by defining entities and updating the schema.

6. Conclusion

GraphQL Federation is a transformative approach for organizations looking to scale their GraphQL services effectively. By enabling teams to work independently while contributing to a unified API, it sets the foundation for a robust and flexible architecture.