Pub-Sub Fan-Out

Your .NET backend streams events into an Azure Event Hub, a stream of location pings, say. Three separate downstream services each need to process every one of those events independently: one calculates a live value, one runs analytics, one checks for anomalies.

All three currently read from the Event Hub through the same consumer group. Event Hub divides the stream's partitions across whoever's in that group, so each service only ever sees a portion of the events, whichever partitions it happens to be assigned.

Multiple independent readers sharing one subscription end up splitting the stream instead of each seeing all of it. That's exactly what pub-sub fan-out fixes.

Pub-sub fan-out gives each service its own full copy of the stream: create a separate consumer group in the Event Hub for each downstream service that needs it, and point each service at its own consumer group instead of a shared one. Each consumer group tracks its own read position, independent of the others, so one service falling behind or restarting never affects what another service receives.

Use: Azure.Messaging.EventHubs (EventHubConsumerClient)

One stream, many independent full copies, one consumer group per reader.

A radio station broadcasts on one frequency. Every radio tuned to that frequency hears the entire broadcast from the moment it tunes in, regardless of how many other radios are also listening.

One radio being turned off or falling behind never changes what any other radio hears.

Many independent listeners, each getting the whole thing, none interfering with the others.