Federation quickstart

In addition to completing this tutorial, you can clone our example gateway on GitHub. The GitHub example is not identical to the gateway you create in this tutorial, but it demonstrates many of the same concepts.

Hello! This tutorial gets you up and running with Apollo Federation. It currently requires Node.js version 12 or 14.

Federation concepts

In a federated architecture, multiple GraphQL APIs are composed into a single federated graph. The individual APIs are called subgraphs, and they're composed into a supergraph:

Usually, each subgraph corresponds to a different service in your backend. The supergraph is then represented by a gateway, which routes each incoming query to the appropriate combination of subgraphs and returns the combined result.

The supergraph's schema is the combination of each subgraph's schema, plus some special federation-specific directives. Each subgraph's schema can even reference and extend types that originate in a different subgraph.

This architecture enables clients to query data from multiple services simultaneously, just by querying the gateway.

Now that we have a high-level understanding of federation concepts, let's jump in.

Example subgraphs

This tutorial uses two Apollo-hosted subgraphs for an example application: a Products subgraph and a Reviews subgraph. Here are their schemas for reference:

1enum CURRENCY_CODE {
2  USD
3}
4
5type Department {
6  category: ProductCategory
7  url: String
8}
9
10type Money {
11  amount: Float
12  currencyCode: CURRENCY_CODE
13}
14
15"""Here are some helpful details about your type"""
16type Price {
17  cost: Money
18
19  """A number between 0 and 1 signifying the % discount"""
20  deal: Float
21  dealSavings: Money
22}
23
24"""
25This is an Entity, docs:https://www.apollographql.com/docs/federation/entities/
26You will need to define a __resolveReference resolver for the type you define, docs: https://www.apollographql.com/docs/federation/entities/#resolving
27"""
28type Product @key(fields: "id") {
29  id: ID!
30  title: String
31  url: String
32  description: String
33  price: Price
34  salesRank(category: ProductCategory = ALL): Int
35  salesRankOverall: Int
36  salesRankInCategory: Int
37  category: ProductCategory
38  images(size: Int = 1000): [String]
39  primaryImage(size: Int = 1000): String
40}
41
42enum ProductCategory {
43  ALL
44  GIFT_CARDS
45  ELECTRONICS
46  CAMERA_N_PHOTO
47  VIDEO_GAMES
48  BOOKS
49  CLOTHING
50}
51
52extend type Query {
53  bestSellers(category: ProductCategory = ALL): [Product]
54  categories: [Department]
55  product(id: ID!): Product
56}

1extend type Product @key(fields: "id") {
2  id: ID! @external
3  reviews: [Review]
4  reviewSummary: ReviewSummary
5}
6
7"""
8This is an Entity, docs:https://www.apollographql.com/docs/federation/entities/
9You will need to define a __resolveReference resolver for the type you define, docs: https://www.apollographql.com/docs/federation/entities/#resolving
10"""
11type Review @key(fields: "id") {
12  id: ID!
13  rating: Float
14  content: String
15}
16
17type ReviewSummary {
18  totalReviews: Int
19  averageRating: Float
20}

1. Install the Rover CLI

Rover is Apollo's CLI for managing graphs, including federated ones.

Install it like so:

1npm install -g @apollo/rover

After installing, run rover in your terminal with no arguments to confirm that it installed successfully. We'll use various Rover commands in later steps.

2. Create a gateway

You can also clone our example gateway on GitHub. The GitHub example is not identical to the gateway you create in this tutorial, but it demonstrates the same concepts.

As mentioned above, your federated supergraph is represented by a gateway that routes queries to various subgraphs. For this tutorial, we'll use some Apollo-hosted example services as our subgraphs, and we'll set up our own gateway in front of them.

With the help of the @apollo/gateway library, Apollo Server can act as our federated gateway.

On your development machine, first create a new project directory for your Node.js gateway. Then inside that directory, run the following to create a package.json file:

1npm init

Next, install the following required libraries:

1npm install apollo-server @apollo/gateway

Finally, create a file named index.js and paste the following into it as a minimal (not-yet-functional) gateway implementation:

1const { ApolloServer } = require('apollo-server');
2const { ApolloGateway } = require('@apollo/gateway');
3
4const supergraphSdl = ''; // TODO!
5
6const gateway = new ApolloGateway({
7  supergraphSdl
8});
9
10const server = new ApolloServer({
11  gateway,
12});
13
14server.listen().then(({ url }) => {
15  console.log(`🚀 Gateway ready at ${url}`);
16}).catch(err => {console.error(err)});

This code demonstrates the basic flow for creating a gateway:

1. We initialize an ApolloGateway instance and pass it the complete composed SDL for our supergraph.

   • Note the TODO. We'll obtain the composed schema in the next section.

2. We initialize an ApolloServer instance and pass it our gateway via the gateway option.

3. We call listen on our server instance to begin listening for incoming requests.

If we run this code as-is with node index.js, we get an error:

1GraphQLError [Object]: Syntax Error: Unexpected <EOF>.

That's because our supergraphSdl is currently empty! Next, we'll compose that schema.

3. Compose the supergraph schema

As a best practice, your gateway should not be responsible for composing its own supergraph schema. Instead, a separate process should compose the schema and provide it to the gateway. This helps improve reliability and reduce downtime when you make changes to a subgraph.

There are multiple ways to compose a supergraph schema from our subgraph schemas:

• On our local machine using the Rover CLI (we'll start with this)

• Via managed federation in Apollo Studio (we'll switch to this in Part 2)

Using managed federation is strongly recommended for production environments. We'll start with local composition to get up and running.

Providing subgraph details

To compose our supergraph schema, the Rover CLI needs the following information about each of our subgraphs:

• The subgraph's schema

• The URL of the subgraph's GraphQL endpoint (which must be accessible by the gateway)

Because we're using Apollo-hosted example subgraphs, we know their endpoint URLs. And Rover can use those URLs to fetch their schemas via a special introspection query.

Configuration file

We provide subgraph details to the Rover CLI in a YAML file. In your project directory, create a file called supergraph-config.yaml and paste the following into it:

1subgraphs:
2  products:
3    routing_url: https://rover.apollo.dev/quickstart/products/graphql
4    schema:
5      subgraph_url: https://rover.apollo.dev/quickstart/products/graphql
6  reviews:
7    routing_url: https://rover.apollo.dev/quickstart/reviews/graphql
8    schema:
9      subgraph_url: https://rover.apollo.dev/quickstart/reviews/graphql

As you can see, we're providing the same URL as the value of two different fields. These fields serve different purposes:

• routing_url is the URL the gateway will use to send GraphQL operations to the subgraph at runtime.

• schema.subgraph_url is the URL that Rover will use to fetch the subgraph schema during composition.

These URLs might theoretically differ. The YAML file also supports providing a subgraph's schema as a local file path, or as a registered graph ref that Rover can fetch from Apollo (for details, see the Rover docs).

Performing composition

Now that our configuration file is ready, we can compose our supergraph schema. To do that, we'll use Rover's supergraph compose command.

From your project directory, run the following command in your terminal:

1rover supergraph compose --config ./supergraph-config.yaml

Rover outputs the following schema:

1schema
2  @core(feature: "https://specs.apollo.dev/core/v0.2"),
3  @core(feature: "https://specs.apollo.dev/join/v0.1", for: EXECUTION)
4{
5  query: Query
6}
7
8directive @core(feature: String!, as: String, for: core__Purpose) repeatable on SCHEMA
9
10directive @join__field(graph: join__Graph, requires: join__FieldSet, provides: join__FieldSet) on FIELD_DEFINITION
11
12directive @join__type(graph: join__Graph!, key: join__FieldSet) repeatable on OBJECT | INTERFACE
13
14directive @join__owner(graph: join__Graph!) on OBJECT | INTERFACE
15
16directive @join__graph(name: String!, url: String!) on ENUM_VALUE
17
18enum core__Purpose {
19  EXECUTION
20  SECURITY
21}
22
23enum CURRENCY_CODE {
24  USD
25}
26
27type Department {
28  category: ProductCategory
29  url: String
30}
31
32scalar join__FieldSet
33
34enum join__Graph {
35  PRODUCTS @join__graph(name: "products" url: "https://rover.apollo.dev/quickstart/products/graphql")
36  REVIEWS @join__graph(name: "reviews" url: "https://rover.apollo.dev/quickstart/reviews/graphql")
37}
38
39type Money {
40  amount: Float
41  currencyCode: CURRENCY_CODE
42}
43
44"""Here are some helpful details about your type"""
45type Price {
46  cost: Money
47
48  """A number between 0 and 1 signifying the % discount"""
49  deal: Float
50  dealSavings: Money
51}
52
53"""
54This is an Entity, docs:https://www.apollographql.com/docs/federation/entities/
55You will need to define a __resolveReference resolver for the type you define, docs: https://www.apollographql.com/docs/federation/entities/#resolving
56"""
57type Product
58  @join__owner(graph: PRODUCTS)
59  @join__type(graph: PRODUCTS, key: "id")
60  @join__type(graph: REVIEWS, key: "id")
61{
62  category: ProductCategory @join__field(graph: PRODUCTS)
63  description: String @join__field(graph: PRODUCTS)
64  id: ID! @join__field(graph: PRODUCTS)
65  images(size: Int = 1000): [String] @join__field(graph: PRODUCTS)
66  price: Price @join__field(graph: PRODUCTS)
67  primaryImage(size: Int = 1000): String @join__field(graph: PRODUCTS)
68  reviewSummary: ReviewSummary @join__field(graph: REVIEWS)
69  reviews: [Review] @join__field(graph: REVIEWS)
70  salesRank(category: ProductCategory = ALL): Int @join__field(graph: PRODUCTS)
71  salesRankInCategory: Int @join__field(graph: PRODUCTS)
72  salesRankOverall: Int @join__field(graph: PRODUCTS)
73  title: String @join__field(graph: PRODUCTS)
74  url: String @join__field(graph: PRODUCTS)
75}
76
77enum ProductCategory {
78  ALL
79  BOOKS
80  CAMERA_N_PHOTO
81  CLOTHING
82  ELECTRONICS
83  GIFT_CARDS
84  VIDEO_GAMES
85}
86
87type Query {
88  bestSellers(category: ProductCategory = ALL): [Product] @join__field(graph: PRODUCTS)
89  categories: [Department] @join__field(graph: PRODUCTS)
90  product(id: ID!): Product @join__field(graph: PRODUCTS)
91}
92
93"""
94This is an Entity, docs:https://www.apollographql.com/docs/federation/entities/
95You will need to define a __resolveReference resolver for the type you define, docs: https://www.apollographql.com/docs/federation/entities/#resolving
96"""
97type Review
98  @join__owner(graph: REVIEWS)
99  @join__type(graph: REVIEWS, key: "id")
100{
101  content: String @join__field(graph: REVIEWS)
102  id: ID! @join__field(graph: REVIEWS)
103  rating: Float @join__field(graph: REVIEWS)
104}
105
106type ReviewSummary {
107  averageRating: Float
108  totalReviews: Int
109}

As you can see, this composed schema includes all of the types and fields from our subgraph schemas, along with many additional directives that the gateway uses to support our federated architecture.

Now, append > supergraph.graphql to the above command to write the composed schema to a file:

1rover supergraph compose --config ./supergraph-config.yaml > supergraph.graphql

4. Start the gateway

We can now edit our index.js file to pull in our composed schema. Replace the file's contents with the following:

1const { ApolloServer } = require('apollo-server');
2const { ApolloGateway } = require('@apollo/gateway');
3const { readFileSync } = require('fs');
4
5const supergraphSdl = readFileSync('./supergraph.graphql').toString();
6
7const gateway = new ApolloGateway({
8  supergraphSdl
9});
10
11const server = new ApolloServer({
12  gateway,
13});
14
15server.listen().then(({ url }) => {
16  console.log(`🚀 Gateway ready at ${url}`);
17}).catch(err => {console.error(err)});

Now with our supergraphSdl properly populated, let's start up the gateway again with node index.js. This time, there's no error!

We can quickly open our browser to studio.apollographql.com/sandbox to explore our composed schema in Apollo Sandbox:

While we're here, you can even execute some test queries against the supergraph.

Nice job! Our supergraph gateway is running locally and communicating with our Apollo-hosted subgraphs.

Next, we'll move our supergraph composition into Apollo Studio so our gateway can pull schema changes dynamically during runtime. On to part 2!