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

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

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"

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.