Option to "deallocate" instead of "delete" when scaling in Azure VMSS

[chilloutman]

Deallocating a VMSS instance means that the VM is only stopped as opposed to deleted. The advantage would be that starting the VM back up should be faster than creating a new one.

From the Azure VMSS FAQ:

• You want to start a set of VMs more quickly than you can scale out a virtual machine scale set.
• Related to this scenario, you might have created your own autoscale engine and want a faster end-to-end scale.

Would this be a useful feature?

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The default behavior should stay "delete". When enabled, a "deallocate" option would have to deallocate instead of delete when scaling in here:

nomad-autoscaler/plugins/builtin/target/azure-vmss/plugin/azure.go

Line 154 in 9c46751

future, err := t.vmss.DeleteInstances(ctx, resourceGroup, vmScaleSet, compute.VirtualMachineScaleSetVMInstanceRequiredIDs{

and, I would expect, first look for deallocated VMs to start before scaling out here:

nomad-autoscaler/plugins/builtin/target/azure-vmss/plugin/azure.go

Line 77 in 9c46751

future, err := t.vmss.Update(ctx, resourceGroup, vmScaleSet, compute.VirtualMachineScaleSetUpdate{

[lgfa29]

Hi @chilloutman 👋

This sounds pretty cool! I didn't know about this feature. It also sounds like a good item for new contributions. Would you be interested in giving it a try? 🙂