Simple cluster autoscaler for AWS Auto Scaling Groups which sets the DesiredCapacity of one or more ASGs to the calculated number of nodes.
Goals:
- support multiple Auto Scaling Groups
- support resource buffer (overprovision fixed or percentage amount)
- respect Availability Zones, i.e. make sure that all AZs provide enough capacity
- be deterministic and predictable
- i.e. the DesiredCapacity is only calculated based on the current cluster state
- scale down slowly to mitigate service disruptions, i.e. at most one node at a time
- support “elastic” workloads like daily up/down scaling
- support AWS Spot Fleet (not yet implemented)
- require a minimum amount of configuration (preferably none)
- keep it simple
This autoscaler was initially created as a proof of concept and born out of frustration with the “official” cluster-autoscaler:
- it only scales up when “it’s too late” (pods are unschedulable)
- it does not honor Availability Zones
- it does not support multiple Auto Scaling Groups
- it requires unnecessary configuration
- the code is quite complex
