Unable to deploy multiple eventhub trigger based azure functions within same function app

Question

When I create multiple eventhub trigger based azure functions within the same function app my azure functions do not behave as expected. I created multiple functions using blueprints approach. Even though each of my azure functions are connected to different eventhubs only the last registered azure function gets triggered no matter whcih eventhub is receiving the event.

Answer 1

This issue is likely due to how the EventHubTrigger functions share the same connection when deployed within a single Function App. Azure Functions using Event Hub triggers operate under the same Event Processor Host, which is a singleton for the entire Function App. This can cause only one of the Event Hub triggered functions to receive and process messages, leading to the behavior where only the last registered function gets triggered.

Possible Causes and Solutions...

Shared Event Processor Host Issue

Azure Functions use the EventProcessorHost internally to manage partitions for Event Hubs. When multiple Event Hub triggers are present in the same Function App, they might end up sharing the same processor, causing them to override each other.

Solution:

• Each function should have a separate consumer group. Event Hub triggers within the same Function App should not use the same consumer group.
• Define separate consumer groups for each function.

Improper Connection String Handling

If all your functions are using the same Event Hub connection string without specifying a unique consumer group, Azure Functions might treat them as the same processor.

Solution: Ensure that each function explicitly uses a separate consumer group in the connection string.

Default Partition Ownership by a Single Function

If multiple functions are trying to process the same Event Hub partitions, only one function will take ownership, leading to other functions not receiving events.

Solution:

• Assign separate consumer groups.
• Deploy separate Function Apps if necessary.

Conclusion

The best way to resolve this issue is to:

1. Assign unique consumer groups for each Event Hub trigger.
2. Ensure each function has a dedicated Event Hub connection string.
3. Consider deploying separate function apps if consumer groups do not solve the issue.

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