Why are events getting dropped in Event Grid in Organisation account?

Question

We have created an azure function with type event grid trigger in our organisation account. The event triggers whenever it recieves telemetry data from IotHub. The endpoint of event grid subscription is the azure function. The data is being sent from IotHub to event grid, but from the event grid the events are getting dropped and are not sent to the azure function. In the dead-lettering, the reason is mentioned as "deadLetterReason":"UndeliverableDueToClientError".MicrosoftTeams-image.png

Answer 1

Hi Gorthi Sai Sri Sindhuja Thanks for reaching out. When Event Grid can't deliver an event within a certain time period or after trying to deliver the event a certain number of times, it can send the undelivered event to a storage account. This process is known as dead-lettering. Event Grid dead-letters an event when one of the following conditions is met.

1. Event isn't delivered within the time-to-live period.
2. The number of tries to deliver the event has exceeded the limit.

Reference: https://learn.microsoft.com/en-us/azure/event-grid/delivery-and-retry#dead-letter-events

The "UndeliverableDueToClientError" error in the dead-lettering of your Event Grid subscription indicates that there was an error in the client (i.e., your Azure Function) most commonly a network issue that prevented the event from being delivered.

The most common reasons for events to be moved to the dead-letter queue are authentication errors, function errors, network errors and function timeouts.

Please verify the client logs, if there are errors or exceptions in your Azure Function code, events may be rejected and moved to the dead-letter queue.

If your Azure Function takes too long to process an event, it may time out and the event may be moved to the dead-letter queue. Make sure that your Azure Function is correctly configured to handle events within the required time limit.

You can also try setting retry policy in azure eventgrid, you can set values for how long Event Grid should try to deliver the event. By default, Event Grid tries for 24 hours (1440 minutes), or 30 times. You can set either of these values for your Event Grid subscription.

Please let me know if you have any further queries.