How do I configure my Apollo Server instance to run in Federation mode?

An ApolloServer instance automatically runs in federation mode when passed the gateway option during instantiation. The gateway option points to an object containing the gateway's configuration, which is created by instantiating a new ApolloGateway() (from the @apollo/gateway library).

Note that the option you pass in to your ApolloServer constructor must be named gateway. If your configuration object is not named gateway, you will need to pass in your configuration like so:

// gateway object.
const gatewayConfig = new ApolloGateway();

const server = new ApolloServer({
  // gateway needs needs to be declared explicitly due to the name of the config object.
  gateway: gatewayConfig,
  /// ... other options
});

Full example and documentation.

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

const gateway = new ApolloGateway();

const server = new ApolloServer({
  gateway,
  // Subscriptions are not currently supported in Apollo Federation
  subscriptions: false,
});

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