Apollo Federation gateway and another server implementation - apollo-server

Question

I am reading about apollo federation and how to migrate from schema stitching and a question came when I read:
The basic strategy for migrating from a stitching gateway to Apollo Federation is to start by making the underlying services federation-capable
https://www.apollographql.com/docs/apollo-server/federation/migrating-from-stitching/#adding-federation-support-to-services
basically federation gateway can't accept another service not federation aware? so there's no way to use federation with another graphql server (such https://github.com/nuwave/lighthouse) or should I misunderstood that line?

Answer 1

Yes, any GraphQL service that's incorporated into the federation gateway has to implement Apollo's federation specification.
Federation relies on the service schema containing several specific types, directives and type extensions:
scalar _Any
scalar _FieldSet
union _Entity
type _Service {
sdl: String
}
extend type Query {
_entities(representations: [_Any!]!): [_Entity]!
_service: _Service!
}
directive #external on FIELD_DEFINITION
directive #requires(fields: _FieldSet!) on FIELD_DEFINITION
directive #provides(fields: _FieldSet!) on FIELD_DEFINITION
directive #key(fields: _FieldSet!) on OBJECT
directive #extends on OBJECT
The service does not have to be a GraphQL.js implementation, but it does need to implement the above additions to the schema as outlined in the spec.

Answer 2

Like #daniel-rearden said it does need to implement additions to the spec.
Check out graphql-transform-federation to assist you with adding the required info. Also check out this blog post

Answer 3

Once you have the server you also need to build the gateway, if you are using docker-compose you can use a reusable docker image as follows:
version: '3'
services:
a:
build: ./a # one service implementing federation
b:
build: ./b
gateway:
image: xmorse/apollo-federation-gateway
ports:
- 8000:80
environment:
CACHE_MAX_AGE: '5' # default cache
ENGINE_API_KEY: '...' # to connect to the apollo engine
POLL_INTERVAL: 30 # to update services changes
URL_0: "http://a"
URL_1: "http://b"
Check out the github repo for a working example.