@apollo/federation

What is @apollo/federation?

@apollo/federation is a library that enables the composition of multiple GraphQL services into a single unified graph. It allows you to build a federated data graph, which can be composed of multiple subgraphs, each managed by different teams or services.

What are @apollo/federation's main functionalities?

Defining a Federated Schema

This code demonstrates how to define a federated schema using @apollo/federation. It includes type definitions and resolvers for a Product type, and sets up an Apollo Server with the federated schema.

const { buildFederatedSchema } = require('@apollo/federation');
const { ApolloServer, gql } = require('apollo-server');

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

  extend type Query {
    product(id: ID!): Product
  }
`;

const resolvers = {
  Product: {
    __resolveReference(product) {
      return { id: product.id, name: "Sample Product" };
    }
  },
  Query: {
    product(_, { id }) {
      return { id, name: "Sample Product" };
    }
  }
};

const server = new ApolloServer({
  schema: buildFederatedSchema([{ typeDefs, resolvers }])
});

server.listen({ port: 4000 }).then(({ url }) => {
  console.log(`🚀 Server ready at ${url}`);
});

Extending Types Across Services

This code demonstrates how to extend types across different services using @apollo/federation. It shows how to add a reviews field to the Product type, which is defined in another service.

const { buildFederatedSchema } = require('@apollo/federation');
const { ApolloServer, gql } = require('apollo-server');

const typeDefs = gql`
  extend type Product @key(fields: "id") {
    id: ID! @external
    reviews: [Review]
  }

  type Review {
    id: ID!
    content: String
  }

  extend type Query {
    reviews(productId: ID!): [Review]
  }
`;

const resolvers = {
  Product: {
    reviews(product) {
      return [{ id: "1", content: "Great product!" }];
    }
  },
  Query: {
    reviews(_, { productId }) {
      return [{ id: "1", content: "Great product!" }];
    }
  }
};

const server = new ApolloServer({
  schema: buildFederatedSchema([{ typeDefs, resolvers }])
});

server.listen({ port: 4001 }).then(({ url }) => {
  console.log(`🚀 Server ready at ${url}`);
});

Gateway Setup

This code demonstrates how to set up an Apollo Gateway to compose multiple federated services into a single graph. It includes a service list with URLs for the products and reviews services.

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

const gateway = new ApolloGateway({
  serviceList: [
    { name: 'products', url: 'http://localhost:4000' },
    { name: 'reviews', url: 'http://localhost:4001' }
  ]
});

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

server.listen({ port: 4002 }).then(({ url }) => {
  console.log(`🚀 Gateway ready at ${url}`);
});

Other packages similar to @apollo/federation

graphql-tools

graphql-tools is a set of utilities from Apollo that can be used to create and manipulate GraphQL schemas. While it does not provide the same level of federation capabilities as @apollo/federation, it is useful for schema stitching and other schema-related tasks.

graphql-mesh

graphql-mesh allows you to use GraphQL to query any service, whether it is a REST API, SOAP, gRPC, or another GraphQL API. It provides a way to unify different data sources into a single GraphQL schema, similar to @apollo/federation, but with a broader range of data source support.

README

Apollo Federation Utilities

Note: If you have arrived here, you are probably looking for the @apollo/subgraph package, which provides the buildSubgraphSchema function for subgraph authors. This package now only contains code for composing subgraphs, which is primarily a gateway and tooling concern.