Federated Subscriptions

GraphQL subscriptions enable your clients to receive real-time data. This is essential for applications that need live updates - like notifications, live chat, stock tickers, collaborative editing, or IoT dashboards.

Hive Router provides full support for federated subscriptions out of the box, with no additional configuration required. It works as a drop-in replacement for other federation routers, making it easy to add real-time capabilities to your federated GraphQL architecture.

How Subscriptions Work

Consider this subscription query against Hive Router:

subscription {
  reviewAdded {
    rating
    body
    author {
      name
    }
  }
}

This creates the following data flow:

Your client executes a subscription operation against Hive Router over HTTP using either Server-Sent Events (SSE) or multipart responses. The router then executes the same subscription against whichever subgraph defines the requested field - in this case, the Reviews subgraph that provides the reviewAdded field. The router communicates with subgraphs using the same protocols: SSE or multipart.

When the Reviews subgraph sends new data, the router receives it and forwards it to the client. If the subscription includes federated entity fields from other subgraphs - like the author field that comes from the Users subgraph in this example - the router automatically resolves those fields by querying the corresponding subgraphs over HTTP. This allows you to subscribe to data that spans multiple subgraphs while maintaining a single subscription connection from your client.

Supported Protocols

Hive Router currently supports two protocols for subscriptions, both for client-to-router and router-to-subgraph communication:

• Server-Sent Events (SSE) - A simple, efficient protocol built on standard HTTP
• Incremental Delivery over HTTP - From the Official GraphQL over HTTP spec RFC
• Multipart HTTP - Based on Apollo’s Multipart HTTP protocol

When dealing with HTTP subscriptions, the router automatically determines which protocol to use based on the Accept header in the request. When subscribing to subgraphs, the router prefers multipart first, then falls back to SSE.

Entity Resolution

One of the most powerful features of federated subscriptions is automatic entity resolution. Your subscription can include fields from multiple subgraphs, and Hive Router handles all the coordination automatically.

subscription {
  reviewAdded {
    # From the reviews subgraph
    id
    body
    rating
    # Entity field from the products subgraph
    product {
      name
      price
    }
    # Entity field from the users subgraph
    author {
      name
      email
    }
  }
}

In this example:

• The reviewAdded subscription is defined in the reviews subgraph
• The product fields are resolved from the products subgraph
• The author fields are resolved from the users subgraph

Hive Router intelligently determines the optimal way to resolve these entity fields, querying the necessary subgraphs as subscription events arrive. This works exactly like entity resolution for regular queries - no special configuration or considerations needed.

Server-Sent Events (SSE)

To use SSE, clients should send requests with the following Accept header:

Accept: text/event-stream

The router will respond with a stream of events implementing the “distinct subscriptions mode” of the GraphQL over SSE spec .

Try It

curl 'http://localhost:4000/graphql' \
  -H 'accept: text/event-stream' \
  --json '{
    "query": "subscription {
      reviewAdded {
        body
        rating
        product {
          name
        }
        author {
          name
        }
      }
    }"
  }'

This command creates an SSE connection and keeps it open to receive new subscription data as server-sent events:

event: next
data: {"data":{"reviewAdded":{"body":"Great product!","rating":5,"product":{"name":"Croissant"},"author":{"name":"Alice"}}}}

event: next
data: {"data":{"reviewAdded":{"body":"Could be better","rating":3,"product":{"name":"Baguette"},"author":{"name":"Bob"}}}}

event: next
data: {"data":{"reviewAdded":{"body":"Excellent quality","rating":5,"product":{"name":"Croissant"},"author":{"name":"Charlie"}}}}

event: complete

This example subscription emits three next events and then sends a complete event to signal the end of the stream. Notice how the product and author fields are automatically resolved from their respective subgraphs.

EventSource

You can easily subscribe over SSE using the browser native EventSource interface. It’s as simple as:

const url = new URL('http://localhost:4000/graphql')
url.searchParams.append(
  'query',
  `subscription {
    reviewAdded {
      body
      rating
      product {
        name
      }
      author {
        name
      }
    }
  }`
)
 
const source = new EventSource(url)
 
source.addEventListener('next', ({ data }) => {
  console.log(data)
})
 
source.addEventListener('error', e => {
  console.error(e)
})
 
source.addEventListener('complete', () => {
  source.close()
})

graphql-sse

We highly recommend using graphql-sse, the zero-dependency, HTTP/1 safe, simple, GraphQL over Server-Sent Events spec client library.

It offers reliable handling of connection management, message parsing, and error handling, as well as silent retries and exponential backoff for improved resilience.

Apollo Client

Please advise the Apollo Client integration recipe.

Relay

Please advise the Relay integration recipe.

urql

Please advise the urql integration recipe.

Incremental Delivery

Using incremental delivery requires clients to send requests with the following Accept header:

Accept: multipart/mixed

The router responds with multipart HTTP responses conforming to the Official GraphQL over HTTP Incremental Delivery over HTTP RFC.

Apollo Client

Relay

meros is a fast utility that makes reading multipart responses simple. It works in both the browser and Node.js.

Using it with Relay is quite straightforward, here’s an example setup:

npm install meros

import { meros } from 'meros/browser'
import { GraphQLResponse, Network, Observable, RequestParameters, Variables } from 'relay-runtime'
 
// Supports both queries/mutations and subscriptions.
function fetchOrSubscribe(operation: RequestParameters, variables: Variables) {
  return Observable.create<GraphQLResponse>(sink => {
    const ctrl = new AbortController()
 
    ;(async () => {
      const parts = await fetch('http://localhost:4000/graphql', {
        signal: ctrl.signal,
        method: 'POST',
        body: JSON.stringify({
          query: operation.text,
          variables
        }),
        headers: {
          'content-type': 'application/json',
          accept: 'application/json, multipart/mixed'
        }
      }).then(meros)
 
      if (parts instanceof Response) {
        // query/mutation
        return parts.json()
      }
 
      // subscription
      for await (const part of parts) {
        sink.next(part)
      }
    })()
      .then(() => sink.complete())
      .catch(error => sink.error(error))
 
    return () => ctrl.abort()
  })
}
 
export const network = Network.create(fetchOrSubscribe, fetchOrSubscribe)

urql

Multipart HTTP

To use multipart responses, clients should send requests with the following Accept header:

Accept: multipart/mixed;subscriptionSpec=1.0

The router will respond with multipart HTTP responses conforming to Apollo’s Multipart HTTP protocol.

Try It

curl 'http://localhost:4000/graphql' \
  -H 'accept: multipart/mixed;subscriptionSpec=1.0' \
  --json '{
    "query": "subscription {
      reviewAdded {
        body
        rating
        product {
          name
        }
        author {
          name
        }
      }
    }"
  }'

This command creates an HTTP multipart request and keeps an open connection that receives new subscription data in response “chunks”:

--graphql
content-type: application/json

{}
--graphql
content-type: application/json

{"payload":{"data":{"reviewAdded":{"body":"Great product!","rating":5,"product":{"name":"Croissant"},"author":{"name":"Alice"}}}}}
--graphql
content-type: application/json

{"payload":{"data":{"reviewAdded":{"body":"Could be better","rating":3,"product":{"name":"Baguette"},"author":{"name":"Bob"}}}}}
--graphql
content-type: application/json

{"payload":{"data":{"reviewAdded":{"body":"Excellent quality","rating":5,"product":{"name":"Croissant"},"author":{"name":"Charlie"}}}}}
--graphql--

This example subscription emits three events and then closes the connection. Notice how the product and author fields are automatically resolved from their respective subgraphs.

Apollo Client

The required headers are automatically added by Apollo Client. Multipart subscriptions are supported out-of-the-box.

npm install @apollo/client graphql rxjs

import { ApolloClient, gql, HttpLink, InMemoryCache } from '@apollo/client'
 
const client = new ApolloClient({
  link: new HttpLink({ uri: 'http://localhost:4000/graphql' }),
  cache: new InMemoryCache()
})
 
client
  .subscribe({
    query: gql`
      subscription {
        reviewAdded {
          body
          rating
          product {
            name
          }
          author {
            name
          }
        }
      }
    `
  })
  .forEach(data => {
    console.log(data)
  })

Relay

We recommend using Incremental Delivery over HTTP with Relay instead.

urql

We recommend using Incremental Delivery over HTTP with urql instead.