User Story

As a user, I would like to specify different expanders for the cluster autoscaler. Having an API field on the ClusterAutoscaler resource to specify the expanders and their precedence will solve this issue for me.

Background

The cluster autoscaler allows users to specify a list of expanders to use when creating new nodes. This list is expressed as a command line flag that takes multiple comma-separated options, eg "--expander=priority,least-waste,random".

We need to add a new field to the ClusterAutoscaler resource that allows users to specify an ordered list of expanders to use. We should limit values in that list to "priority", "least-waste", and "random" only. We should limit the length of the list to 3 items.

Steps

• add a new API field for expander options
• write unit tests to confirm behavior in CAO

Stakeholders

• openshift eng

Definition of Done

• user can express priority, least-waste, and random expanders through the ClusterAutoscaler resource

• Docs
• need docs on the expanders, what they are, how to select them
• need docs describing how to configure the priority expander

• Testing
• we will add unit tests in this card, e2e tests will follow in another card