[Federation] How to merge schema from gateway itself.

In short, is there a way to implement Apollo Federation such that the gateway itself has it’s own schema?

(EDIT) TLDR No, the gateway can’t also be a federated service.

Federating Apollo Server where the gateway itself has a schema

@apollo/gateway@0.6.5 @apollo/federation@0.6.2

Expected Behavior

When I am instantiating my Apollo Gateway server, I expect that I should be able to merge schemas from federated services, as well as the schema from the gateway itself.

Actual Behavior

The gateway server fails to mount the /graphql route because it is expecting all of the services to be currently running before it does so.

On run time, the following error is printed to the console:

POST /graphql 404 11.251 ms - 147
Encountered error when loading gateway at http://localhost:8000/graphql: invalid json response body at http://localhost:8000/graphql reason: Unexpected token < in JSON at position 0
[DEBUG] Fri Jun 07 2019 12:11:07 GMT-0400 (Eastern Daylight Time) apollo-gateway: Configuration loaded for Gateway
[DEBUG] Fri Jun 07 2019 12:11:07 GMT-0400 (Eastern Daylight Time) apollo-gateway: Composing schema from service list:
  remote-svc
TypeError: schema.toConfig is not a function
    at Object.composeServices (/gateway-app/node_modules/@apollo/federation/dist/composition/compose.js:191:67)
    at Object.composeAndValidate (/gateway-app/node_modules/@apollo/federation/dist/composition/composeAndValidate.js:13:41)
    at ApolloGateway.createSchema (/gateway-app/node_modules/@apollo/gateway/dist/index.js:90:47)
    at ApolloGateway.<anonymous> (/gateway-app/node_modules/@apollo/gateway/dist/index.js:81:22)
    at Generator.next (<anonymous>)
    at fulfilled (/gateway-app/node_modules/@apollo/gateway/dist/index.js:4:58)
    at process._tickCallback (internal/process/next_tick.js:68:7)

Source Code

const url = new URL(`redis://${REDIS_URL}:${REDIS_PORT}/${REDIS_DATABASE}`).toString()

const cache = new RedisCache({ url })

const context = ({ req }) => {
  if (!(req.user || req.headers.authorization === ROUTE_AUTH)) {
    throw new AuthenticationError('Not authenticated')
  }
  return { user: req.user, req: req }
}

try {
  const loadGateway = async () => {
    try {
      const { schema, executor } = await gateway.load()
      return { schema, executor }
    } catch (err) {
      console.error(err)
      return null
    }
  }

  const gateway = new ApolloGateway({
    debug: process.env.ENV !== 'prod',
    serviceList: [
      { name: 'gateway', url: `${GATEWAY_HOSTNAME}/graphql` },
      { name: 'remote-svc', url: `${REMOTE_SERVICE_HOSTNAME}/graphql` },
    ],
  })

  const { schema, executor } = loadGateway()
  const server = new ApolloServer({
    schema,
    executor,
    cache,
    dataSources,
    engine: { apiKey: ENGINE_API_KEY },
    tracing: true,
    context,
  })
  server.applyMiddleware({ app })
} catch (err) {
  console.error(err)
}

Justification

The reason for implementing our gateway server this way is to primarily for ease of authentication.

Our gateway server performs all authentication so that we do not have to expend an unnecessary round trip to authenticate a user before executing their request.

[hnq90]

After migration from Schema Stitching to Federation, we tried several ways to keep the Gateway keeps its own schema. We couldn’t separate the schema away the Gateway for some reasons. Finally, we have to start 2 GraphQL server in same server with different port and path. The Federation GraphQL server must be run before Gateway GraphQL server started.

• Federation GraphQL Server: /graphq-extended on port 3001.
• Apollo Gateway Server: /graphql on port 3000.

We haven’t found any better solution but currently it works 🥇 🔥

Here’s the implementation:

export async function runFederationServer({ PORT: portFromEnv = DEFAULT_PORT }) {
  const path = '/graphql-extended'
  const app: express.Application = express()
  // ...
  const serviceSchema = buildFederatedSchema(gatewaySchema.schemas)
  const server = new ApolloServer({
    schema: serviceSchema,
    context: ({ req, res }) => { /* */ }
  })
  
  return app
}

export async function runServer({ PORT: portFromEnv = DEFAULT_PORT, GRAPHQL_ENDPOINTS: graphqlEndpoints = '' } = {}) {
  const path = '/graphql'
  const app: express.Application = express()
  // ...
  const serviceList = [
   {
     name: 'Extended Schema',
     uri: 'http://0.0.0.0:3001/graphql-extended',
   },
   {
     // Other Federation GraphQL servers
   },
  ]
  const gateway = new ApolloGateway({
    serviceList,
    buildService({ url }) { /* */ }
  })
  
  return app
}

runFederationServer(process.env).then(runServer(process.env))

[calebfaruki]

I’ll jump to a conclusion here based on the naming of your service: are you trying to run the gateway at port 8000 and treat it as a federated service at the same time? If so, that’s not going to work; the gateway has to resolve all schemas before it can compose the final schema.

Exactly that.

Okay, so the solution here is to move the schema from the gateway server to another service.

Thanks for confirming that!