Function app service bus trigger is working only intermittently

Question

Function app service bus trigger is working only intermittently

Matt Atkins 0

I have a number of function apps running on flex consumption plan, and using service bus triggers.

All of the apps and infrastructure is created through automation, so all are configured identically.

On just one of the apps, the service bus trigger is only operational some of the time - it seems to have periods of 'downtime' where the service bus is not polled, so messages are not actioned.

I also have a timed trigger, which periodically accesses the same service bus, and those requests are still working, so the service bus side seems fine, connectivity between the two fine, and the issue is on the app side.

During the periods of downtime, even restarting the app makes no difference.

The downtime can clearly be seen, by checking the graph of requests on the service bus side. The requests are very regular (every 10 seconds) when it is working, and drops to zero when not working, which can be for several hours at a time.

All other apps with same config are working fine, with no downtime / drop outs in service bus calls.

There are no errors in App Insights.

As this issue is currently only affecting one app, could it be a local fault with the app service host?

Pravallika KV 10,415 Reputation points Microsoft External Staff Moderator

2026-02-24T10:26:18.03+00:00
Hi @Matt Atkins ,

Thanks for reaching out to Microsoft Q&A.

Please check the below possibilities:

Verify that the connection settings are correctly configured. Ensure that your function app includes the ServiceBusConnection environment variable and that it points to the correct Service Bus namespace. A missing or incorrect connection string can lead to sporadic triggers.

Since you're using a flexible consumption plan, keep in mind that it may not handle service bus triggers as effectively as premium plans. If other apps with the same configuration are functioning correctly, consider the scaling behavior for your specific app. The flexible consumption plan can introduce delays in message processing, especially if there are load spikes or issues on the host side.

Check Application Insights for unusual patterns or errors that might not be apparent from just looking at the app. Use the queries referenced in the documentation to look for any startup exceptions or invocation failures.

If there are other functions or instances of your app that are potentially polling the same service bus, it may cause your specific instance to appear idle. Ensure that your setup avoids competing triggers that might affect each other's ability to process messages.

If you’ve confirmed everything is configured correctly but the issue persists, it might be worth checking the health of the app service host. There could be temporary issues with the underlying infrastructure affecting just that instance of your function app.

Hope this helps!
Matt Atkins 0 Reputation points

2026-02-24T12:07:17.05+00:00

Hi @Pravillika thanks for this... For 1-4 there is nothing showing - and it seems 5 is more relevant - an issue with the app service host or underlying infrastructure.
I don't see much I can do to check or diagnose this though - when I navigate to the function app service plan (this is the 'host' right?) in Azure Portal, there is very little information or functionality available.
What can I do to further diagnose the host or underlying infrastructure?
Pravallika KV 10,415 Reputation points Microsoft External Staff Moderator

2026-02-24T12:11:48.0966667+00:00

Thanks for the confirmation @Matt Atkins . I have reached out to you over private message. Could you please check and confirm?