Auto Reload of gateway for schema changes in federated service apollo GraphQL - graphql

Question

In Apollo Federation, I am facing this problem:
The gateway needs to be restarted every time we make a change in the schema of any federated service in service list.
I understand that every time a gateway starts and it collects all the schema and aggregates the data graph. But is there a way this can be handled automatically without restarting the Gateway as it will down all other unaffected GraphQL Federated services also
Apollo GraphQL , #apollo/gateway

Answer 1

There is an experimental poll interval you can use:
const gateway = new ApolloGateway({
serviceList: [
{ name: "products", url: "http://localhost:4002" },
{ name: "inventory", url: "http://localhost:4001" },
{ name: "accounts", url: "http://localhost:4000" }
],
debug: true,
experimental_pollInterval:3000
})
the code above will pull every 3 seconds

Answer 2

I don't know other ways to automatically reload the gateway other than polling.
I made a reusable docker image and i will keep updating it if new ways to reload the service emerge. For now you can use the POLL_INTERVAL env var to periodically check for changes.
Here is an example using docker-compose:
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' # seconds
POLL_INTERVAL: '30' # seconds
URL_0: "http://a"
URL_1: "http://b"

Answer 3

You can use express to refresh your gateway's schema. ApolloGateway has a load() function that go out to fetch the schemas from implementing services. This HTTP call could potentially be part of a deployment process if something automatic is needed. I wouldn't go with polling or something too automatic. Once the implementing services are deployed, the schema is not going to change until it's updated and deployed again.
import { ApolloGateway } from '#apollo/gateway';
import { ApolloServer } from 'apollo-server-express';
import express from 'express';
const gateway = new ApolloGateway({ ...config });
const server = new ApolloServer({ gateway, subscriptions: false });
const app = express();
app.post('/refreshGateway', (request, response) => {
gateway.load();
response.sendStatus(200);
});
server.applyMiddleware({ app, path: '/' });
app.listen();
Update: The load() function now checks for the phase === 'initialized' before reloading the schema. A work around might be to use gateway.loadDynamic(false) or possibly change gateway.state.phase = 'initialized';. I'd recommend loadDyamic() because change state might cause issues down the road. I have not tested either of those solutions since I'm not working with Apollo Federation at the time of this update.