autoscaler-webhook

Example Webhook Autoscaler Service

This service provides an example of the webhook fleetautoscaler service which is used to control the number of GameServers in a Fleet (Replica count).

Autoscaler Service

The service exposes an endpoint which allows client calls to custom scaling logic.

When this endpoint is called, target Replica count gets calculated. If a fleet does not need to scale we return Scale equals false. Endpoint receives and returns the JSON encoded FleetAutoscaleReview every SyncPeriod which is 30 seconds.

Note that scaling up logic is based on the percentage of allocated gameservers in a fleet. If this fraction is more than threshold (i. e. 0.7) then Scale parameter in FleetAutoscaleResponse is set to true and Replica value is returned increased by the scaleFactor (in this example twice) which results in creating more Ready GameServers. If the fraction below the threshold (i. e. 0.3) we decrease the count of gameservers in a fleet. There is a minReplicasCount parameters which defined the lower limit of the gameservers number in a Fleet.

To learn how to deploy the fleet to GKE, please see the tutorial Create a Fleet (Go).

Example flow

1. Fleet with 100 Replicas (gameservers) was created.
2. 70 gameservers got allocated -> No scaling for now.
3. One more server allocated, we got 71 allocated gameservers, fraction in a fleet is over 0.7 AllocatedPart > 0.7 so we are scaling by scaleFactor. Which results in doubling fleet size.
4. Fleet now has 200 Replicas.
5. AllocatedPart = 71/200 = 0.355 so no downscaling for now.
6. 22 gameservers were shutdown and now this count of gameservers is not in Allocated state.
7. AllocatedPart = 59/200 = 0.295 Thus AllocatedPart < 0.3 and fleet got scaled down. Fleet now return to 100 gameservers size.