Azure Function doesn't trigger by IOT Hub

Question

Azure Function doesn't trigger by IOT Hub

Pavel Livshits 10

Hello,

I have an issues with triggering functions by events from iothub edge devices. I need to run two functions that would listen on Edge device events but triggered according to the some quarry.

For that purpose on the IOT hub side I have created 2 Event Hubs with full shared access policies, 2 endpoints and 2 routes without any routing queries so at the beginning that both functions will get all the events, later I'll do the filtering. On the function side both functions are configured to be triggered by their own set.

@EventHubTrigger(name = "message1", eventHubName = "event1", connection = "AzureIotHubEvent1", consumerGroup = "$Default", cardinality = Cardinality.MANY)

@EventHubTrigger(name = "message2", eventHubName = "event2", connection = "AzureIotHubEvent2", consumerGroup = "$Default", cardinality = Cardinality.MANY)

However, no matter what I do only one function is getting events and the other getting nothing. I have checked and rechecked the configuration but it's haven't found anything there. Moreover, both Event Hubs Instances are getting the all the events.

Any idea what might be the problem and how to debug it?

Thanks,

Pavel

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Answer 1

LeelaRajeshSayana-MSFT 17,866 Moderator

Hi @Pavel Livshits Greetings! Welcome to Microsoft Q&A forum. Thank you for posting this question.

The publish/subscribe mechanism of Event Hubs is enabled through consumer groups. A consumer group is a view (state, position, or offset) of an entire event hub. Consumer groups enable multiple consuming applications to each have a separate view of the event stream, and to read the stream independently at their own pace and with their own offsets.

Instead of using the $Default consumer group to process Events routed to the Event Hub, create two unique consumer groups, one for each end point. Provide the created consumer group name in the function consumerGroup attribute. You can create the consumer group through your Azure Portal under the Built-in endpoints of your IoT Hub. Please refer the below image

consumer group

I have also noticed that you are using a "cardinality" attribute in your EventHubTrigger function. I could not find a reference of this attribute in the official documentation of Event Hub Trigger I appreciate it if you can provide a reference of the resource where you have obtained this attribute from.

Please let us know if information shared is useful. Reach out to us if you still face issues and we would be glad to assist you.

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Pavel Livshits 10 Reputation points

2023-01-19T22:21:40.78+00:00

Hi @LeelaRajeshSayana-MSFT

Thanks you for your answer and kind words.

First, regarding your questions about carnality attribute, I have found it here https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-event-iot-trigger?tabs=in-process%2Cfunctionsv2%2Cextensionv5&pivots=programming-language-java#example

Now I did try your proposal to use different consumer groups and it works well. Thanks!

However, when I asked regarding using two different topics, my idea was to filter functions by queries so only the relevant functions will be triggered accordingly.

Is it possible to do the same with one topic but different consumer groups?

Thanks,

Pavel
LeelaRajeshSayana-MSFT 17,866 Reputation points Moderator

2023-01-19T22:36:53.32+00:00

Hi @Pavel Livshits greetings! Thank you for your response and sharing the reference to the Java help center link. I was referring to .NET language section and could not find the cardinality parameter.

Could you provide more details on your approach when you say filter functions later using queries? It is beneficial to filter data using the routing query option when setting up the Message Routing. This ensures that only the data that matches the criteria would end up in the Event Hub and trigger the linked function. Please refer the below image showing a routing query

It is highly recommended to follow this approach so that the end points will not be overloaded with same duplicate messages and the Azure Functions does not get triggered for every message the Event Hub receives. Please utilize the following resource IoT Hub message routing query syntax which provides different samples on how you can create a routing query.

Please let us know if you need any additional details or assistance with formulating the routing query. Kindly do not forget to do Mark the answer as useful so that community members with similar issues will benefit.
Pavel Livshits 10 Reputation points

2023-01-21T14:37:14.51+00:00

Hi @LeelaRajeshSayana-MSFT

The query approach is exactly what I need. However, I'm not sure how it would be possible to apply it if I have two functions that triggered by same event but only have different consumerGroup. In my case each function suppose to handle different type of message but if I put query it would be on same topic for both functions so still both function will be triggered. Am I right?

Eventually, what I would like to do is to trigger function for specific type of message. Is it possible id both functions are listening to the same topic but different consumer groups?

Thanks,

Pavel
LeelaRajeshSayana-MSFT 17,866 Reputation points Moderator

2023-01-24T23:53:32.3033333+00:00

Hi @Pavel Livshits apologies for the delayed update on this. Using two different consumer groups does not impact the routing of the data to the event hubs. Consumer groups enable multiple consuming applications such as Event Hubs to each have a separate view of the event stream, and to read the stream independently at their own pace and with their own offsets.

In my case each function suppose to handle different type of message but if I put query it would be on same topic for both functions so still both function will be triggered. Am I right?

In the question you posted, you stated that you have 2 Event Hubs created, once assigned to each Azure Function. The messages routed to this Azure Event Hubs are what triggers the Azure Functions and not consumer groups.

I do not follow what you mean by Topic. Do you mean same IoT device data source point? You can create multiple routes on the same Data source Device Telemetry Messages to route the messages to multiple Event Hubs using Routing Query. Functions will be triggered only when a message is received on the Event Hub.

Eventually, what I would like to do is to trigger function for specific type of message. Is it possible id both functions are listening to the same topic but different consumer groups?

This is absolutely possible by creating two routing queries to send the data to the Events Hubs you have.

I would be glad to assist you further on this if you can share a sample of your device telemetry data your IoT Hub is receiving and the use case when Function 1 and Function 2 should be triggered.

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Azure Function doesn't trigger by IOT Hub

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