Exam AZ-104 topic 4 question 96 discussion

Minute 0-15: Memory usage exceeds 70%. Autoscale rule triggered. Instance count increased by 1 (from 2 to 3). Cooldown period starts. Minute 15-20 (Cooldown Period): No further scaling can occur during the cooldown period. Minute 20-30: Memory usage continues to exceed 70%, but the cooldown is still in effect. No further scaling during this time.

Completely correct, we have to remember that the original duration is used the first or if it resets because the number went below the threshold to trigger scale action. If it never goes below at any point, then we just wait for Cool Down and then reevaluate again or add another instance. I actually messed up again and used the duration but that is an error.

here a reference about "look back": https://learn.microsoft.com/en-us/azure/azure-monitor/autoscale/autoscale-understanding-settings#autoscale-evaluation

This is correct according to this article: https://cloudbuild.co.uk/azure-virtual-machine-scale-set-duration-and-cool-down-explained/

Answer D. for the scaler to kick in, it needs to be 15 minutes of average use above x % that is set. so once the load starts, it will wait 15 minutes until that rule is met, and a scale up will happen. once it scales up at the 15 minute mark, the 5 minute cooldown starts. at 20 minute mark, the scaler will LOOK BACK at the PAST 15 minutes to see if during that time the usage was still higher than x% and scale up again. then it will wait another 5 minutes, check the PAST 15 minutes again, scale up again, etc. etc. the previous performance data doesnt get thrown out after each scale, it keeps on sliding the dataset its checking forward. imagine if this was a real app and you get hit by huge traffic surge. like your company release a new product. what this would do in your method is scale up one instance every 20 minutes, so it might mean multiple hours of degraded performance while it catches up to demand, while the reality and my explanation, it would kick in after 15 minutes and then keep scaling every 5 minutes which is a much faster and reasonable solution.

No, if after the cool down period the threshold is stil met, then the next scale out operation will happpen immediately (followed by another cool down period, of course). "The cooldown period for each rule dictates how long after the previous scale action (whatever rule initiated was), the rule can be applied." Source: https://github.com/MicrosoftDocs/azure-docs/issues/17169

its Box1: 3 Box2: 1