Performance drop off in Azure function elastic premium plan

Question

I have decided to try the premium plan to avoid cold start performance penalties. However I have noticed that performance still fades if a function is inactive for a small period. Am I missing some configuration?

Answer 1

@George Aggrey Premium Plan tackles cold starts by having at-least one instance active and then at-least one-prewarmed (until the max scale-out limit) which are instances that have already been started up.

So, after being inactive for a while, the number of instances go down and if there is a sudden surge in requests, more than what the warmed instances can handle could cause performance issues while the app is scaled out to the required amount.

But since the number of ready and pre-warmed instances can be configured, you will just have to configure them accordingly.

Answer 2

In this case there could have been no performance surge. I have one straw function with which I performed a series of tests. In the first test I run it every 20 minutes, second test every minute and lastly every 5 seconds. For all plans the first call after a period of inactivity was always significantly slower. I went to the trouble of noting the process ID of the instance.

Answer 3

The dedicated plan performed the best as we would expect, but there was still difference. I am looking to keep latency well below 100ms from the get go.