Azure Container Apps with KEDA + Azure Service Bus scaling to 0 even when messages are coming in

[mxvoloshin]

Hi,

I'm using Azure Container Apps with a custom KEDA-based scaling rule that listens to an Azure Service Bus queue.

Here’s my setup:

minReplicas: 0

maxReplicas: 2

pollingInterval: 30 seconds

cooldownPeriod: 300 seconds

The scaling generally works — it scales up when messages arrive and down when idle.

However, I’m seeing unexpected scale-to-zero behavior even when messages are still coming in (though sporadically).

📈 My scenario:
Messages arrive with irregular frequency: 1 message every 1 to 15 seconds.

Each message is processed very quickly, so the queue often appears empty when KEDA checks it.

As a result, the app sometimes scales to 0 before the full 300-second cooldown, even though messages continue to trickle in.

❓ My question:
Is my assumption correct that because messages are processed too quickly, KEDA may not "see" them during the polling intervals — causing it to believe the queue is empty and trigger scale-down?

If so, is there a recommended way to prevent this kind of premature scale-down for low-frequency but steady message traffic?

Thanks in advance!

[rickbrouwer]

Interesting case!

I think you are right. If messages are processed faster than the polling interval, KEDA sees an empty queue and starts the scale-down timer, even though more messages are coming.
Would it be a good idea to use scaledJobs for this, so the job handles a message? Or do you really want scaledObjects?