Apollo Gateway/Federation does not work to graphql-mesh backend service

[nicerobot]

Describe the bug

I've tried a custom Apollo Server and the default graphql-mesh dev server and my Apollo Gateway fails when connecting to the server. If i run the backend service using postgraphile server, federation works fine.

The error from the gateway is

(node:50191) UnhandledPromiseRejectionWarning: Error: A valid schema couldn't be composed. The following composition errors were found:
        Unknown type: "_Entity".
        [api] Subscription -> `Subscription` is an extension type, but `Subscription` is not defined in any service
        Unknown type "_Entity".
    at ApolloGateway.createSchemaFromServiceList (.../node_modules/@apollo/gateway/dist/index.js:490:19)
    at ApolloGateway.updateByComposition (.../node_modules/@apollo/gateway/dist/index.js:345:48)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async ApolloGateway.updateSchema (.../node_modules/@apollo/gateway/dist/index.js:323:13)
    at async ApolloGateway.loadDynamic (.../node_modules/@apollo/gateway/dist/index.js:302:13)
    at async ApolloGateway.load (.../node_modules/@apollo/gateway/dist/index.js:273:15)
    at async SchemaManager.start (.../node_modules/apollo-server-core/dist/utils/schemaManager.js:42:28)
    at async ApolloServer._start (.../node_modules/apollo-server-core/dist/ApolloServer.js:146:30)
    at async ApolloServer.listen (.../node_modules/apollo-server/dist/index.js:67:9)

To Reproduce
Steps to reproduce the behavior:

1. This .meshrc.yaml (and a postgres connection)

sources:
  - name: api
    handler:
      postgraphile:
        schemaName:
          - public
        appendPlugins:
          - "postgraphile-federation-plugin"
          - "postgraphile-plugin-connection-filter"
          - "@graphile/pg-aggregates"

Run mesh dev

The above server works great by itself. But trying to run it behind an apollo gateway reports the above error

2. Create a simple gateway

const { ApolloServer } = require('apollo-server');
const { ApolloGateway } = require("@apollo/gateway");
const gateway = new ApolloGateway({serviceList: [{ name: 'api', url: 'http://localhost:4000/graphql' }]});
const server = new ApolloServer({gateway, subscriptions: false});
server.listen().then(({ url }) => { console.log(`Server ready at ${url}`); });

3. Run it and get the error above.
4. Shutdown the gateway
5. Shutdown the graphql-mesh server
6. Run postgraphile directly using the same plugins

postgraphile \
  --port 4000 \
  --schema public \
  --append-plugins postgraphile-federation-plugin,postgraphile-plugin-connection-filter,@graphile/pg-aggregates

7. Run the above gateway again and notice it starts just fine and can query the backend service through the gateway port

Expected behavior

The gateway should work.

Environment:

• OS: macOS BigSur
• NodeJS: v12.22.2

"dependencies": {
	"@apollo/federation": "^0.33.8",
	"@graphile/pg-aggregates": "^0.1.0",
	"@graphql-mesh/cli": "^0.45.0",
	"@graphql-mesh/grpc": "^0.19.1",
	"@graphql-mesh/openapi": "^0.23.3",
	"@graphql-mesh/postgraphile": "^0.18.0",
	"@graphql-mesh/transform-filter-schema": "^0.14.8",
	"@graphql-mesh/transform-naming-convention": "^0.9.0",
	"@graphql-mesh/transform-rename": "^0.11.8",
	"@graphql-mesh/transform-prefix": "^0.9.8",
	"@grpc/grpc-js": "^1.4.6",
	"@grpc/proto-loader": "^0.6.9",
	"apollo-server": "^3.6.1",
	"apollo-server-core": "^3.6.1",
	"apollo-server-express": "^3.6.1",
	"aws-sdk": "^2.1051.0",
	"compression": "^1.7.4",
	"express": "^4.17.2",
	"glob": "^7.2.0",
	"google-protobuf": "^3.19.2",
	"graphile-build": "^4.12.2",
	"graphile-build-pg": "^4.12.2",
	"graphql": "^15.8.0",
	"graphql-jit": "^0.7.2",
	"graphql-tag": "^2.12.6",
	"js-yaml": "^3.14.1",
	"pg": "^8.7.1",
	"postgraphile": "^4.12.8",
	"postgraphile-federation-plugin": "^0.6.0",
	"postgraphile-plugin-connection-filter": "^2.2.2",
	"unzipper": "^0.10.11",
	"winston": "^3.3.3"
},
"resolutions": {
	"graphql": "^15.8.0",
	"postgraphile-federation-plugin": "^0.6.0"
},

Additional context

[ardatan]

We no longer support custom servers, and a lot of things changed and improved in the latest packages. I couldn't test it because you didn't provide a reproduction but I think it should be fixed in the latest versions.
Let us know if the issue still persists then we can reopen the issue.