Function's Event Hub trigger rarely executes the function

Question

Hello,

We have a C#(.NET 8) Azure function triggered by Event Hub. There are a lot of incoming messages but rarely triggers the function and the the outgoing messages are a tenth of incoming messages. There are no errors in the Log Anaytics workspace and also nothing in function's App Insights. I guess nothing will be in App Insights as the function isn't executed enough.

I also changed throughput and Azure function only logs a string to App Insights. Previously, we tried to send logs to our Enterprise Splunk where we started seeing the issue. So we reverted back everything in function to just log a string in App Insights.

Do you believe there is something lingering behind from when we deployed Splunk? I disabled the function and restarted the function app. Also re-deployed just in case.

How else can I debug the issue?

Thanks.

Answer 1

Hello dotnet_guy,

Welcome to the Microsoft Q&A and thank you for posting your questions here.

Problem

I understand regarding your scenarios that your C#.NET 8 Azure function triggered by Event Hub and not executing as expected.

Solution

So far, if your Azure Function triggered by Event Hub isn't executing as expected, I don't think you need to guess or leave any stone untouched. If all you've done to troubleshoot are correct and you're sure, then:

1. Create a new consumer group in your Event Hub and use it in your Azure Function. Sometimes using the default consumer group can lead to unexpected behavior. Verify that your function is using the correct consumer group in the function.json configuration.
2. Understand how Event Hubs scale in your chosen plan (Consumption or Premium). For Consumption and Premium plans, scaling decisions are based on Target Based Scaling. Ensure your configuration aligns with your expected load. https://learn.microsoft.com/en-us/answers/questions/1234971/azure-function-not-triggering-when-deployed-but-wo
3. Although you reverted back to logging only to App Insights, ensure that there are no lingering configurations or dependencies related to Splunk. Double-check your deployment files and settings.
4. Monitor your Function App using Azure Monitor. Check for any anomalies, spikes, or patterns. Use Application Insights to track function executions, dependencies, and exceptions. Set up custom metrics if needed.
5. Consider implementing retry policies in your function to handle transient errors. You can use built-in retry attributes or implement custom retry logic.
6. Finally, If you need access to event metadata (such as enqueued time, sequence number, etc.), bind to an EventData object in your function. You can also use binding expressions in the method signature to access these properties

Accept Answer

I hope this is helpful! Do not hesitate to let me know if you have any other questions.

** Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful ** so that others in the community facing similar issues can easily find the solution.

Best Regards,

Sina Salam

Answer 2

Hello @dotnet_guy ,

welcome to this moderated Azure community forum.

I checked the attributes and one possible explanation is that the consumergroup is not unique enough.

The Azure Function is a consumer of the EventHub.

Each consumer wants a copy of the same incoming message.

This is established by giving each consumer its own consumergroup.

Unfortunally, a lot of documentation and tooling uses the default available $default so reusing the same consumergroup is a common problem.

Please use a specific consumergroup and try again.

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