Demonstration app for federated services

Just another example app for Federated graphs usage within Apollo Gateway, or Graphql-Mesh.

Why?

1. To have a quick reference to "what is it?"-answers;
2. To have a minimal installation for experiments and upgrades;
3. To demonstrate supergraph power in rails application context;
4. To study the pros/cons of both: graphql mesh and apollo gateway;

What?

This application includes two extra-simple rails api-only applications, to serve the federated subgraphs on the /graphql endpoints, our setup will be able to compose them both to a supergraph schema that will be used to launch our gateway.

Quick start

Launch backend services:

git clone git@github.com:AndreyIlyunin/federated-rails-app.git
cd federated-rails-app

docker-compose up --build

Setup db:

cd federated-rails-app

docker-compose exec users rails db:create db:migrate db:seed
docker-compose exec articles rails db:create db:migrate db:seed

Compose graphql schema:

cd gateway

npm install -g @apollo/rover
rover supergraph compose --config ./supergraph-config.yaml > supergraph.graphql

Launch gateway with node index.js

Reproduce

Create api-only rails applications (as much as you need):

rails new AppName --api

extend them with some models:

rails g model EntityName field:type

add graphql dependencies to these projects:

# https://github.com/rmosolgo/graphql-ruby
gem 'graphql'
# https://github.com/Gusto/apollo-federation-ruby
gem 'apollo-federation'

run: bundle install and: rails generate graphql:install, this generate some code to the app/graphql dir, we will also need to clean up all of the exampled "test"-query and mutations, just because they are repeated in both applications, and federated schemas say 'NO' to query/type repeats. the last step is to create initial entities for graphql:

rails g graphql:object EntityName

That is it. Subgraph services are ready to start as separate graphql servers.

To make them "federated", you will require to complete those steps: https://github.com/Gusto/apollo-federation-ruby#getting-started for both of applications.

To merge them in a supergraph, we will need to use apollo-gateway:

We will use the simplest way to start (in my opinion). Those steps are well documented here: https://www.apollographql.com/docs/federation/gateway/ but this is the fast-growing tech stack, and tools changes quickly, and just to take a snap:

mkdir gateway && cd gateway

npm install -g @apollo/rover # this one is required to compose sub-graphs into supergraph
npm install @apollo/gateway apollo-server graphql # this is the server with the gateway
touch index.js
touch subgraph-config.yaml 

index.js

const { ApolloServer } = require('apollo-server');
const { ApolloGateway } = require('@apollo/gateway');
const { readFileSync } = require('fs');

const supergraphSdl = readFileSync('./supergraph.graphql').toString();

const gateway = new ApolloGateway({
    supergraphSdl
});

const server = new ApolloServer({
    gateway,
});

server.listen().then(({ url }) => {
    console.log(`🚀 Gateway ready at ${url}`);
}).catch(err => {console.error(err)});

subgraph-config.yaml

Make sure you know the ports for appropriate apps, in this example we run the users app on :3000, and the articles - :3001, there is no matter which port or name to choose at this point.

subgraphs:
  users:
    routing_url: http://localhost:3000/graphql
    schema:
      subgraph_url: http://localhost:3000/graphql
  articles:
    routing_url: http://localhost:3001/graphql
    schema:
      subgraph_url: http://localhost:3001/graphql

As you can mention, the gateway launched using the ./supergraph.graphql file. We can create it by spinning our services and composing from subgraphs:

rails s # or `rails s -p 3001` with different port to launch both in parallel

to generate the supergraph schema with rover cli (2.0.0):

rover supergraph compose --config ./supergraph-config.yaml > supergraph.graphql

and launch the gateway:

node index.js

you can use any of graphql clients (the GraphiQL extension for your browser for simply-fast setup) and use the http://localhost:4000 endpoint to refer the apollo server with the gateway on aboard.