GraphQL subscriptions offer real-time data updates to clients. Apollo Router now supports self-hosted instances enabling subscriptions over WebSocket and HTTP.
The Role of Subscriptions in GraphQL
Subscriptions in GraphQL are operations allowing clients to receive real-time data, ideal for time-sensitive applications like stock trading or live sports updates. Unlike queries and mutations, subscriptions are long-lasting, meaning they can deliver multiple updates over time.
How They Work
GraphQL subscriptions operate by maintaining a persistent connection between the client and server. The Apollo Router facilitates executing these subscriptions against relevant subgraphs and returning the updates using a WebSocket subprotocol or an HTTP-callback protocol.
An example Subscription Request:
subscription OnStockPricesChanged {
stockPricesChanged {
...
}
}
In response, the server does not send a single response. Instead, it sends multiple pieces of data as they become available, allowing clients to stay updated in real-time.
Configuring Apollo Router for Subscriptions
Prerequisites
Before enabling subscriptions on Apollo Router, you need to:
- Update Apollo Router instances to at least version 1.22.0.
- Ensure your router is part of a GraphOS Enterprise organization.
- Update your Apollo Federation to version 2.4 or later.
- Modify your subgraph schemas to support Apollo Federation 2.4, adding necessary directives.
- Update to Apollo Server version 4 for implementing subgraph.
Setting up the Router
Apollo Router's YAML configuration file needs to be updated with the communication protocols for handling subscriptions. The router supports various WebSocket subprotocols and an HTTP-callback protocol based on the subgraphs' expectations.
WebSocket Setup Example:
subscriptions:
over_websocket:
# subgraph configuration details...
HTTP Callback Setup Example:
public_url: https://example.com:4000/callback
Special Considerations
Any update to the supergraph schema causes all active subscriptions to terminate. Clients can detect this and initiate a new subscription.
Subscription Deduplication
Apollo Router can deduplicate subscriptions, reducing the load by using one connection for multiple identical subscriptions.
Subscription Termination on Schema Update
With every supergraph schema update, Apollo Router terminates active subscriptions, requiring clients to reconnect.
Advanced Configuration and Management
WebSocket Authentication Support
Apollo Router can propagate HTTP Authorization headers as connection parameters for WebSocket handshakes with subgraphs.
Event Queue Capacity
To manage a high volume of events, Apollo Router maintains an in-memory event queue, configurable for each active subscription.
Limiting Client Connections
You can set the maximum number of open subscription connections to prevent overloading the router's resources.
In conclusion, Apollo Router's support for GraphQL subscriptions expands its capability to cater to real-time data requirements. Its flexible configuration options for WebSocket and HTTP protocols, along with features like subscription deduplication and event queue management, make it a dependable choice for GraphQL-based enterprise solutions.
Tags:
- #GraphQL
- #ApolloRouter
- #RealTimeData
- #Subscription
- #EnterpriseFeature
https://www.apollographql.com/docs/router/executing-operations/subscription-support/