Is custom storage polling relevant to consumption plan Azure Functions?

Question

How does the concept of storage queue polling apply when an Azure Function is hosted under the consumption plan?

I get the principal of polling with classic hosted WebJob functions and I understand that the maximum polling interval of 1 minute can be overridden. However in the case of consumption plan hosting there is no app-level memory resident process, therefore I assume that Azure internals spin up a FunctionApp via some other trigger beyond my control.

The motivation for this question is that I am trying to understand typical E2E function invocation propagation delays when an Azure hosted WebApp adds a message to a storage queue. In my case the WebApp, StorageQueue and pre-compiled function DLL will run in the same Azure region.

I need to cap Azure Function invocation delays to under 10 seconds with an average of <3 seconds.

Answer 1

Unfortunately this isn't possible on the consumption plan with the current polling model, as we poll your trigger resource every 10s to determine if there are new events requiring a function instance to be loaded/started.

If your function app runs frequently enough that it always has active instances (a new queue message every 5 min, for example) you can get the invocation delays that you want, as the instances themselves handle the polling.

The worst case (no function instances running) is ~10s polling + ~5s instance startup time to process a new event.