README.md

Apollo Federation Node Gateway — Example

This example shows a small Apollo gateway (running on port 4000) that composes two subgraphs:

• users service (port 4001)
• posts service (port 4002)

The example uses the Node interface and helper utilities from @profusion/apollo-federation-node-gateway and a shared TypeIDDataSource to encode/decode IDs.

Quick start

Requirements: Node.js (16+), Yarn (used by this project).

First, we need to build the current version of the lib. From the root directory run:

yarn install && yarn build && yarn pack --out profusion-apollo-federation-node-gateway.tgz

Now, from the example/ folder run:

yarn install

Before starting the gateway, start the subgraph services. The subgraph services are in src/services/users.ts and src/services/posts.ts — run them in separate terminals using Yarn and ts-node:

# in one terminal (users)
yarn ts-node src/services/users.ts

# in another terminal (posts)
yarn ts-node src/services/posts.ts

# after both services are running, start the gateway
yarn start

Server endpoints started by the example:

• Gateway: http://localhost:4000/graphql
• Users subgraph: http://localhost:4001/graphql
• Posts subgraph: http://localhost:4002/graphql

Example GraphQL queries

Below are example queries you can run against the gateway (http://localhost:4000/graphql).

• Fetch all users and their last post:

query Users {
  users {
    id
    username
    lastPost {
      id
    }
  }
}

• Fetch all posts with author info:

query Posts {
  posts {
    id
    title
    body
    author {
      id
      username
    }
  }
}

• Use the Node interface to fetch a single entity by node id. The example project encodes type IDs via TypeIDDataSource.

Example Node query (replace the id with one returned from the users or posts lists above):

query NodeQuery($id: ID!) {
	node(id: $id) {
    __typename
		id
		... on User {
      username
		}
		... on Post {
			title
			body
		}
	}
}

Variables

{
	"id": "<PASTE_NODE_ID_HERE>"
}

HTTP requests

Below are example request bodies and descriptions you can paste into any client like Postman or Bruno (use POST to the GraphQL endpoint).

1. Get users with last post

POST http://localhost:4000/graphql

Headers:

• Content-Type: application/json

Body (raw JSON):

{
  "query": "query GetUsersWithLastPost { users { id username lastPost { id } } }"
}

2. Get posts with author

POST http://localhost:4000/graphql

Headers:

• Content-Type: application/json

Body (raw JSON):

{
	"query": "query GetPostsWithAuthor { posts { id title body author { id username } } }"
}

3. Node query (GraphQL + variables)

POST http://localhost:4000/graphql

Headers:

• Content-Type: application/json

Body (raw JSON):

{
	"query": "query NodeQuery($id: ID!) { node(id: $id) { id ... on User { username } ... on Post { title body } } }",
	"variables": { "id": "<PASTE_NODE_ID_HERE>" }
}

Tip: When you run users or posts queries the example services return encoded node IDs using TypeIDDataSource (for example VXNlcjox-style ids). Use one of those values in the Node query variables.

Using the Node interface programmatically

If you are using the @profusion/apollo-federation-node-gateway library directly in Node code, the example shows how to use createNodeResolver and nodeInterface in your subgraphs and NodeGateway to wire the gateway.

Key pieces from the example:

• src/typeIDDataSource.ts — creates a TypeIDDataSource with per-type prefixes.
• src/services/users.ts and src/services/posts.ts — each subgraph uses createNodeResolver(typeIDDataSource) to provide Node resolution helpers and includes the nodeInterface typeDefs.
• src/index.ts — creates new NodeGateway({ typeIDDataSource }, { supergraphSdl: new IntrospectAndCompose({ subgraphs: [...] }) }) and passes it to ApolloServer as gateway.

Troubleshooting

• If the gateway can't reach the subgraphs, ensure the subgraphs are running on ports 4001 and 4002 and that any firewall or proxy allows local connections.
• If you see unexpected IDs, the example uses TypeIDDataSource to encode ids; inspect src/typeIDDataSource.ts for the configured prefixes.