Azure function does not scale over 20 instances

Jason Le 96 Microsoft Employee

I am running azure function event hub trigger on function premium plan. Event hub has 32 partitions, cpu percentage is high, but Azure function only scale to 20 instances(+1 for balancing). Service plan is in south central US.

1 answer

MayankBargali-MSFT 68,656 Reputation points

2021-02-12T10:25:43.717+00:00

Hi @Jason Le

Can you please confirm if the OS is windows or linux. The limit is 20 for Central US for linux OS in each region and OS configuration
If you want to increase this limit you can open a support ticket.

Reference: https://learn.microsoft.com/en-us/azure/azure-functions/functions-premium-plan?tabs=portal#region-max-scale-out
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Jason Le 96 Reputation points Microsoft Employee

2021-02-12T19:43:12.097+00:00

It's windows, and I already set max burst to 100

MayankBargali-MSFT 68,656 Reputation points

2021-02-15T09:05:42.62+00:00

@Jason Le Azure Functions uses a component called the scale controller to monitor the rate of events and determine whether to scale out or scale in. Scale controller works differently for HTTP and event based triggers. In the above screenshot, I can see live metrics for the last 60 sec. Further, I don't constant load and the CPU ranges from (70% to 90%) within 60 seconds. Based on the scale controller monitor metrics it will see if a new instance is needed or not. This needs to be looked at from backend logs to see if one more instance was needed during that time.

Jason Le 96 Reputation points Microsoft Employee

2021-02-16T17:41:29.443+00:00

I think there is a 20 instance cap, because it runs 20 instances constantly. Do you know where should I contact to look into backend logs?
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