Subscriptions

Streams of events

A subscription operation keeps a connection open and pushes results to the client when events occur, such as an order status changing or a chat message arriving. Transports are typically WebSockets (the graphql-ws protocol) or server-sent events. On the server, resolvers subscribe to an event source (a pub/sub system such as Redis or Kafka in multi-instance deployments). Authorise subscriptions at connection time and per event, and consider whether polling or simpler server-sent events would suffice.

Subscribing to order updates

A client subscription.

subscription OrderUpdates($orderId: ID!) {
  orderStatusChanged(orderId: $orderId) {
    id
    status
    updatedAt
  }
}

Use a shared pub/sub with several servers

An in-memory event emitter only reaches clients connected to the same server instance.

त्वरित जाँच: Which transport is commonly used for GraphQL subscriptions?

• FTP
• WebSockets
• SMTP
• Plain HTTP GET without streaming