kube-aws-autoscaler

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