In a microservices architecture, the concept of federation allows multiple GraphQL services to be combined into a single federated graph. Apollo Gateway is a popular solution for implementing federation in JavaScript applications using Apollo Server.

Let’s walk through the steps to implement federation with Apollo Gateway.

Step 1: Set Up the Gateway Server

First, create a new JavaScript project and install the necessary packages:

npm init -y
npm install apollo-server apollo-gateway

Create a file named gateway.js and set up the Apollo Gateway server:

const { ApolloGateway } = require("@apollo/gateway");

const gateway = new ApolloGateway({
  serviceList: [
    { name: "accounts", url: "http://localhost:4001/graphql" },
    { name: "products", url: "http://localhost:4002/graphql" },
    // Add more services as needed
  ],
});

// Start the server
gateway.listen().then(({ url }) => {
  console.log(`Gateway server ready at ${url}`);
});

Replace the url values with the URLs of your individual GraphQL services.

Step 2: Create Individual GraphQL Services

Create separate GraphQL services for each microservice. For example, create an accounts service in a file named accounts.js:

const { ApolloServer, gql } = require("apollo-server");

const typeDefs = gql`
  type User {
    id: ID!
    name: String!
    email: String!
  }

  type Query {
    user(id: ID!): User
  }
`;

const resolvers = {
  Query: {
    user: (parent, { id }, context) => {
      // Logic to fetch user from database or API
    },
  },
};

const server = new ApolloServer({ typeDefs, resolvers });

server.listen(4001).then(({ url }) => {
  console.log(`Accounts service ready at ${url}`);
});

Similarly, create a products service in a file named products.js with relevant type definitions, resolvers, and listen on a different port.

Step 3: Start the Services and Gateway

Open separate terminals for each service and the gateway.

1. Terminal 1: Start the accounts service with node accounts.js.
2. Terminal 2: Start the products service with node products.js.
3. Terminal 3: Start the gateway with node gateway.js.

Step 4: Verify the Federated Graph

Open a browser and navigate to http://localhost:PORT/graphql (replace PORT with the port number specified in the gateway.js file).

Execute queries against the federated graph, combining data from different services:

query {
  user(id: "1") {
    id
    name
    email
  }
}

You should see the combined results from the accounts and products services.

Congratulations! You have successfully implemented federation with Apollo Gateway in JavaScript.

#hashtags: #ApolloGateway #Federation