MAGNUM: Cluster autoscaler support for manually removed node from node group

[mkleku81]

Description:
Magnum cluster-autoscaler in case of manually removed node from node group, can remove all nodes from the node group before the autoscaler removes the correct node.

Version:
Cluster Autoscaler: v1.27.5,v1.29.5
Cloud Provider: Magnum

Current Behavior:
Magnum cluster autoscaler fails to retrieve ID of manually removed node during resize on cleanup

I0128 10:03:19.798126       1 magnum_manager_impl.go:397] resizeOpts: node_count=4, remove=[]

Expected Behavior:
The Magnum autoscaler will be able to retrieve the ID of a manually deleted node, which in this case is a fake node with the prefix openstack:/// not fake:///.
https://github.com/kubernetes/autoscaler/blob/cluster-autoscaler-release-1.27/cluster-autoscaler/cloudprovider/magnum/magnum_manager_impl.go#L379-L386

Reproduction Steps:
Create a magnum cluster (k8s ver 1.27 ,1.29 ) with cluster autoscaler (v1.27.5,v1.29.5) running with log level 5 .
Add to it node group.
Add a workload that scales a node group to, say, 4 nodes.
Remove manualy the first node in the node group(by openstack server delete ...).
The autoscaler will start cleaning up random nodes, by resizing without ID nodes to remove

kubectl logs cluster-autoscaler-9bf47d569-bsdsn -f  | grep resizeOpts
I1221 15:37:37.541377       1 magnum_manager_impl.go:397] resizeOpts: node_count=4, remove=[]
I1221 15:37:53.991168       1 magnum_manager_impl.go:397] resizeOpts: node_count=3, remove=[]
I1221 15:38:10.812047       1 magnum_manager_impl.go:397] resizeOpts: node_count=2, remove=[]
I1221 15:38:27.103804       1 magnum_manager_impl.go:397] resizeOpts: node_count=1, remove=[]

which, in a pessimistic case like the one above, may result in the clearing of all nodes in node group.

Describe the solution you'd like:
Add here
https://github.com/kubernetes/autoscaler/blob/cluster-autoscaler-release-1.27/cluster-autoscaler/cloudprovider/magnum/magnum_manager_impl.go#L379-L386

support for fake nodes with the prefix openstack:///
e.g. like this

		if nodeRef.IsFake {
			if strings.HasPrefix(nodeRef.Name, "fake:///") {
			    _, index, err := parseFakeProviderID(nodeRef.Name)
			    if err != nil {
			    	return fmt.Errorf("error handling fake node: %v", err)
			    }
			    nodesToRemove = append(nodesToRemove, index)
			    continue
			} else if strings.HasPrefix(nodeRef.Name, "openstack:///") { 
			    nodeID , err := parseFakeProviderIDDeletedNode(nodeRef.Name)
			    if err != nil {
			    	return fmt.Errorf("error handling fake node: %v", err)
			    }
			    nodesToRemove = append(nodesToRemove, nodeID)
			    continue
			}
		}

where parseFakeProviderIDDeletedNode is an additional util function like this

func parseFakeProviderIDDeletedNode(id string) (string, error) {
	id2 := strings.TrimPrefix(id, "openstack:///")
	return id2, nil
}

Additional context:
After looking in the code in the main branch, I see that there this case will also occur.

[adrianmoisey]

/area cluster-autoscaler