cloud provider clusterapi with cloud-provider-azure AzureMachinePools using orchestrationMode=Flexible does not scale down

[desek]

Which component are you using?:

cluster-autoscaler

What version of the component are you using?:

Component version: 1.28.2

What k8s version are you using (kubectl version)?:

kubectl version Output

$ kubectl version
Client Version: v1.28.4
Server Version: v1.28.4

Also using CAPZ version: 1.10.8

What environment is this in?:

• The CAPI/CAPZ Management cluster is running on Azure AKS.
• The workload cluster is running in Azure.
• The cluster-autoscaler is running on the Management cluster

What did you expect to happen?:

When cluster-autoscaler taints nodes for deletion it will delete them and scale down the MachinePool.

What happened instead?:

cluster-autoscaler can't find the Machines

How to reproduce it (as minimally and precisely as possible):

Assuming you have a running CAPZ cluster:

1. Create an AzureMachinePool with spec.orchestrationMode set to Flexible
2. Scale out a deployment that triggers cluster-autoscaler to increase the replica count of the MachinePool
3. CAPZ will create one AzureMachinePoolMachine resource per required node
4. Scale in a deployment that trigger cluster-autoscaler to initiate the scale-down process
5. cluster-autoscaler fails scale-down due not finding Machine resources

Step 5 fails due to VMSS Flex replicas are created as AzureMachinePoolMachine and not Machine.

Anything else we need to know?:

This commit adds the required resources, indexers and conditions in handlers to correctly remove unneeded AzureMachinePoolMachines: https://github.com/LiveArena/kubernetes-autoscaler/commit/b819ed9bf27722146805425ab82ea5f860c990b3

[Shubham82]

/area provider/azure /area provider/cluster-api

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[Shubham82]

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