{AKS} az aks update: Fix --outbound-type validation for UDR and userAssignedNATGateway

[FumingZhang]

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Related command

Fixes Azure/azure-cli#33204

The CLI incorrectly required --vnet-subnet-id when updating outbound type to userDefinedRouting or userAssignedNATGateway. This parameter is not registered for 'aks update', creating an impossible state for users.

Changes:

• In UPDATE mode, when vnet_subnet_id is empty, raise a clear InvalidArgumentValueError explaining that updating to UDR/ userAssignedNATGateway is only supported for BYO VNet clusters
• In CREATE mode, preserve existing RequiredArgumentMissingError
• For BYO VNet clusters, the subnet is already known from the agentpool, so validation passes and the update works correctly
• Added 4 unit tests covering CREATE and UPDATE scenarios

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[azure-client-tools-bot-prd]

Hi @FumingZhang,
Please write the description of changes which can be perceived by customers into HISTORY.rst.
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[yonzhan]

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

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[github-actions]

Hi @FumingZhang

Release Suggestions

Module: aks-preview

• Update VERSION to 20.0.0b3 in src/aks-preview/setup.py

Notes

• For more info about extension versioning, please refer to Extension version schema

[Copilot]

Pull request overview

Fixes az aks update --outbound-type validation so updating to userDefinedRouting / userAssignedNATGateway no longer incorrectly requires --vnet-subnet-id (which isn’t registered for update), and instead emits a clear error for unsupported managed-VNet clusters.

Changes:

• Adjust outbound type validation to raise InvalidArgumentValueError (UPDATE) vs RequiredArgumentMissingError (CREATE) when vnet_subnet_id is absent.
• Add unit tests for update/create validation scenarios around UDR and user-assigned NAT gateway.
• Document the behavior change in HISTORY.rst.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/aks-preview/azext_aks_preview/managed_cluster_decorator.py	Updates outbound-type validation logic to differentiate CREATE vs UPDATE behavior when subnet info is missing.
src/aks-preview/azext_aks_preview/tests/latest/test_managed_cluster_decorator.py	Adds tests covering update/create paths for UDR and userAssignedNATGateway.
src/aks-preview/HISTORY.rst	Adds changelog entry describing the improved update-time error behavior.