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openkruise / kruise-game

Game Servers Management on Kubernetes
https://openkruise.io/kruisegame/introduction
Apache License 2.0
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[proposal] Autoscaler Improvement #63

Closed chrisliu1995 closed 1 year ago

chrisliu1995 commented 1 year ago

Background

OKG autoscaler is implemented according to Keda's external scaler mechanism, which provides two interfaces, GetMetricSpec exposes Target, and GetMetrics exposes Value.

The current autoscaler of OKG uses the number of replicas of GameServerSet as Target in the GetMetricSpec method, and uses the number of replicas minus the number of WaitToBeDeleted as Value in the GetMetrics method. Since the calls of GetMetricSpec and GetMetrics are asynchronous, this will lead that, at some moments, the replicas obtained in GetMetricSpec and GetMetrics is not the same, and then, the desired replicas calculated by HPA does not meet expectations.

Improvement

An improvement method is proposed to fix the target value set by GetMetricSpec, whether to scale down or not is completely determined by GetMetrics, and change the type of the scaler from Value to AverageValue. After the improvement, the ratio of value to target will only be less than or equal to 1, and the scaling-down will only be performed when the ratio is less than 1, which solves the current problem of occasional unexpected scaling-up.

chrisliu1995 commented 1 year ago

@smartwang @ringtail

We can discuss that issue here.