why scale event triggers the opposite scale event in flapping

Question

why scale event triggers the opposite scale event in flapping

Answer 1

Mayank Jain, Apologies for the delayed response.

Flapping is just a name given to scenario when opposite scaling events are triggered based on the auto-scale setting. The following documentation has sample example which explains this event with more details - Flapping in Autoscale.

For the settings mentioned in the question, consider a scenario of the following 2 auto-scale setting -

memory%>=80 increased by 1
memory%>=50 decrease by 1

When first scenario is evaluated to be TRUE, it is also true for second scenario. Generally, scale-out and scale-in use the opposite operators, like

Scale in - when memory% < 60
Scale out - when memory% > 80.

The autoscale controllers evaluate the condition for scaling operation and may even skip it if there are chances of flapping occurring. Based on the auto scale settings shared in the questions, are you experiencing flapping? Examining the activity logs should help understand if you are impacted by this scenario - https://learn.microsoft.com/en-us/azure/azure-monitor/autoscale/autoscale-flapping#log-files

Hope this helps.