Support for OS Disk Type in AKSNodeClass

[nandorKollar]

Fixes #801

Description

This change adds a new option to AKSNodeClass to specify the required OS disk type.

How was this change tested?

• Ran make az-all, created an AKS with non-default OS disk type, which worked fine.
• Added new unit test to verify both validation of this new option as well as verify that the value is properly used when provisioning a VM.

Does this change impact docs?

• Yes, PR includes docs updates
• Yes, issue opened: #
• No

Release Note

New feature: support for OS Disk Type in AKSNodeClass

[alex-hunt-materialize]

@nandorKollar I think there might be some conflicts between this PR and my PR #1339, just because we both want to use the same field name in the AKSNodeClass. I think mine is less specific, and therefore would make more sense with the osDiskType field name.

Can I ask you to change your field name to something more specific? Maybe something like osManagedDiskStorageAccountType? That way, if someone ever implements the third related task of specifying which ephemeral disk type (NVMe, Cache, Resource), we could call that field osEphemeralDiskPlacementType and we'd have nice consistency in the naming. In that case, my osDiskType field would specify which of the other fields matters.

In my proposal:

1. osDiskType would be for specifying whether the OS disk should be Managed or EphemeralWithFallbackToManaged.
2. osManagedDiskStorageAccountType would be for the storage account type of the OS disk if using a managed disk (Premium_LRS, etc...).
3. osEphemeralDiskPlacementType would be for the placement type of the OS disk if ephemeral (NVMe, Cache, Resource).

No one has offered to implement the third thing, but there is a ticket open for it, which my PR only partially addresses.

[nandorKollar]

@nandorKollar I think there might be some conflicts between this PR and my PR #1339, just because we both want to use the same field name in the AKSNodeClass. I think mine is less specific, and therefore would make more sense with the osDiskType field name.

Can I ask you to change your field name to something more specific? Maybe something like osManagedDiskStorageAccountType? That way, if someone ever implements the third related task of specifying which ephemeral disk type (NVMe, Cache, Resource), we could call that field osEphemeralDiskPlacementType and we'd have nice consistency in the naming. In that case, my osDiskType field would specify which of the other fields matters.

In my proposal:

1. osDiskType would be for specifying whether the OS disk should be Managed or EphemeralWithFallbackToManaged.
2. osManagedDiskStorageAccountType would be for the storage account type of the OS disk if using a managed disk (Premium_LRS, etc...).
3. osEphemeralDiskPlacementType would be for the placement type of the OS disk if ephemeral (NVMe, Cache, Resource).

No one has offered to implement the third thing, but there is a ticket open for it, which my PR only partially addresses.

Thanks @alex-hunt-materialize for noticing this name collision. Sure, I can rename the field. It seems that indeed we need two different configuration parameter: one is for selecting between Ephemeral (if available)/Managed, that's what your PR does, and maybe one to select a different manage instance type (this is osManagedDiskStorageAccountType), that I try to address here, and probably we need a followup PR for osEphemeralDiskPlacementType? Actually this approach diverges from AKS a bit, as far as I know there's no way to select a managed disk type, every node is created with PremiumSSD (at least that's what I recall), therefore I'm curious about the opinion of the maintainers of this project.