{AKS} az aks update: Fix the bug affecting VMAS to VMS migration

[FumingZhang]

---

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Related command

{AKS} az aks update: Fix the bug affecting VMAS to VMS migration. The code recently added to official azure-cli is updating the value of nodepool type earlier than the code in aks-preview, leading to the following error. The fix is to slightly relax the check conditions in aks-preview.

          raise CLIError('This is not a valid VMAS cluster, we cannot proceed with the migration.')

E knack.util.CLIError: This is not a valid VMAS cluster, we cannot proceed with the migration.

• [AKS] az aks update: Support VMAS to VMS agent pool migration in AKS commands azure-cli#31831
• https://dev.azure.com/azclitools/public/_build/results?buildId=262770&view=logs&j=155127ab-52f1-52e7-0e45-625d9d7884a4&t=4bb67950-ef03-52d4-44f5-d1a8cd56c919&l=3677

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[yonzhan]

Thank you for your contribution! We will review the pull request and get back to you soon.

[Copilot]

Pull Request Overview

This PR fixes a bug in the VMAS to VMS migration functionality within the az aks update command. The fix addresses an issue where the migration validation was too restrictive, preventing valid migration scenarios from proceeding.

Key changes:

• Updated version number from 18.0.0b19 to 18.0.0b20
• Modified the agent pool type validation logic to accept both CONST_AVAILABILITY_SET and CONST_VIRTUAL_MACHINES types
• Added corresponding entry to the changelog documenting the bug fix

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
setup.py	Version bump to 18.0.0b20
managed_cluster_decorator.py	Fixed validation logic for VMAS to VMS migration to accept additional valid agent pool types
HISTORY.rst	Updated changelog with bug fix description and reorganized version entries

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[Release] Update index.json for extension [ aks-preview-18.0.0b20 ] : https://dev.azure.com/msazure/One/_build/results?buildId=131608261&view=results