how to retry when call retryQueue.AddSync () also fails?

Question

I am using Azure Function EventHub trigger. The messages coming to EH are very critical and we don't want to miss any. If while processing message from my Event Hub, something happens, I write to my retryQueue as follows:

try
{
     await retryQueue.AddAsync (some data from my hub); 
    // if this call also fails, it goes to my catch
}
catch (exception e)
{
    await retryQueue.AddAsync (my eventData); 
    // but what if this call also fails?
}

But what happens when AddAsync() call also fails in my catch block? How and where do I save the message for processing later? Is there such thing as IsTransient (which is available in my Service bus queue)?

In theory, if you fall back to the same Storage account that is used to store progress/offsets, they should either both work or both fail. I don't have enough practical experience though. — Mikhail Shilkov, Mar 01 '18 at 20:42

score 0 · Answer 1 · answered Mar 02 '18 at 07:59

Tolerance for duplicates - If check-pointing fails due to timeout/partition least lost not the error in your function code, then the next EventProcessorHost that gets a lease on that partition will start retrieving messages from the last known checkpoint.

Event Hub guarantees at-least-once delivery but not at-most-once delivery.

Azure Functions will not attempt to change that behavior. If not having duplicate messages is a priority, then you will need to mitigate it in your workflow. As such, when check-pointing fails, there are more duplicate messages to manage if your Function is processing messages at batch level.

For more details, refer to this case.

how to retry when call retryQueue.AddSync () also fails?

1 Answers1