Two different Service Bus queue trigger function apps with same service bus name and queue

Question

Hi, I have two service bus queue triggers function apps with same service bus name and queue details, but pointing to different destinations. Is it possible for both service bus functions to get triggered for the same message and send the message twice?

Answer 1

Hello @Azure-search !

Yes, it is indeed possible to have multiple Azure Functions triggered by the same message from an Azure Service Bus queue.

However, the default behavior of Azure Service Bus is to use a "peek-lock" receive mode. This means when a function pulls a message from the queue, it is locked and made invisible to other receivers for a certain period of time. The function needs to complete (acknowledge) the message within this period, otherwise the message becomes visible again and can be processed by another function.

In your case, if you have two different Function Apps listening to the same queue, the message will be processed by one of them first (due to the lock). Once that Function App completes processing and acknowledges the message, the message will be removed from the queue. Consequently, the other Function App won't see or process that message.

If you want both Function Apps to process the same message, you would need to handle this differently. One way could be to use a Service Bus Topic instead of a Queue. Topics support publish/subscribe semantics, meaning a single message sent to the Topic can be received by multiple subscribers (each subscriber receives a copy of the message). This way, you can have multiple Function Apps each subscribing to the Topic and processing the messages independently.

https://learn.microsoft.com/en-us/azure/service-bus-messaging/service-bus-queues-topics-subscriptions

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