aks-preview: Support VMSS agent pool VM size resize via nodepool update by wenhug · Pull Request #9732 · Azure/azure-cli-extensions

wenhug · 2026-03-26T21:14:06Z

Summary

Enable changing the VM size (SKU) of an existing VMSS-based agent pool via az aks nodepool update --node-vm-size <new-size>.

When the user changes the VM size of a VMSS node pool, the AKS RP performs a rolling upgrade:

Surge new nodes with the target VM size
Cordon and drain old nodes
Delete old nodes

This is a preview feature that requires:

AFEC registration: Microsoft.ContainerService/AgentPoolVMSSResize
RP internal toggle: enable-agentpool-vmsize-resize (currently enabled for E2E + Canary)

The --node-vm-size parameter already existed on nodepool update for VirtualMachines pool autoscaler updates. This PR extends it to also work for VMSS pools.

Usage

# Resize VM size for a VMSS node pool
az aks nodepool update \
  -g MyResourceGroup \
  -n nodepool1 \
  --cluster-name MyManagedCluster \
  --node-vm-size Standard_D4s_v3

RP-side validation

The RP validates the resize request and blocks incompatible combinations:

DiskControllerType (SCSI vs NVMe)
CPU Architecture (x64 vs ARM64)
Confidential Computing (SNP)
Hypervisor Generation (V1 vs V2)
Combined with K8s version upgrade or node count change

Changes

agentpool_decorator.py: Add update_vm_size() method for VMSS pools and integrate it into update_agentpool_profile_preview()
_params.py: Mark --node-vm-size as is_preview=True for nodepool update
_help.py: Update help text and add VMSS resize CLI example
test_agentpool_decorator.py: Add unit tests for update_vm_size

Test plan

Unit tests added for update_vm_size (both Standalone and ManagedCluster modes)
E2E test exists in AKS RP repo (Scenario_VMSS_VMSize_Resize)
Manual validation with preview AFEC registration

azure-client-tools-bot-prd · 2026-03-26T21:14:10Z

️✔️Azure CLI Extensions Breaking Change Test

️✔️Non Breaking Changes

azure-client-tools-bot-prd · 2026-03-26T21:14:13Z

Hi @wenhug,
Please write the description of changes which can be perceived by customers into HISTORY.rst.
If you want to release a new extension version, please update the version in setup.py as well.

yonzhan · 2026-03-26T21:15:10Z

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

github-actions · 2026-03-26T21:15:10Z

The git hooks are available for azure-cli and azure-cli-extensions repos. They could help you run required checks before creating the PR.

Please sync the latest code with latest dev branch (for azure-cli) or main branch (for azure-cli-extensions).
After that please run the following commands to enable git hooks:

pip install azdev --upgrade
azdev setup -c <your azure-cli repo path> -r <your azure-cli-extensions repo path>

github-actions · 2026-03-26T21:16:29Z

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github-actions · 2026-03-26T21:19:51Z

Hi @wenhug

Release Suggestions

Module: aks-preview

Update VERSION to 19.0.0b30 in src/aks-preview/setup.py

Notes

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

Copilot

Pull request overview

This PR extends az aks nodepool update --node-vm-size to support resizing VMSS-based agent pools (preview), aligning CLI behavior with the RP’s rolling-replacement resize flow.

Changes:

Add a VMSS-aware update_vm_size() path to the nodepool update decorator and wire it into update_agentpool_profile_preview().
Mark --node-vm-size as a preview parameter for aks nodepool update and update CLI help text/examples accordingly.
Add unit tests validating update_vm_size() behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
`src/aks-preview/azext_aks_preview/agentpool_decorator.py`	Adds `update_vm_size()` and invokes it during preview nodepool update assembly.
`src/aks-preview/azext_aks_preview/_params.py`	Marks `--node-vm-size` as preview for `aks nodepool update`.
`src/aks-preview/azext_aks_preview/_help.py`	Updates help text and adds a VMSS resize example.
`src/aks-preview/azext_aks_preview/tests/latest/test_agentpool_decorator.py`	Adds unit tests for `update_vm_size()`.

src/aks-preview/azext_aks_preview/agentpool_decorator.py

src/aks-preview/azext_aks_preview/tests/latest/test_agentpool_decorator.py

wenhug · 2026-03-26T21:36:08Z

Addressed the two Copilot review comments:

Comment 1 (blocker in update_auto_scaler_properties): Good catch! Removed the InvalidArgumentValueError that rejected --node-vm-size for VMSS pools. That guard was added when --node-vm-size was VMs-pool-only, but now VMSS pools support VM size resize via rolling upgrade.

Comment 2 (VMs pool test): Added a third test case verifying update_vm_size() is a no-op for VirtualMachines pools (handles both Standalone and ManagedCluster decorator modes).

Also added a HISTORY.rst entry per the bot's request.

FumingZhang · 2026-03-27T00:01:56Z

/azp run

azure-pipelines · 2026-03-27T00:02:09Z

Azure Pipelines successfully started running 2 pipeline(s).

FumingZhang

lgtm

src/aks-preview/HISTORY.rst

FumingZhang · 2026-03-30T03:49:37Z

Please resolve merge conflict and rebase/merge from main to pass the CI checks, @wenhug

Enable changing the VM size (SKU) of an existing VMSS-based agent pool via `az aks nodepool update --node-vm-size <new-size>`. The RP performs a rolling upgrade (surge new nodes, drain old, delete old) to replace nodes with the new VM size. This preview feature requires: - AFEC registration: Microsoft.ContainerService/AgentPoolVMSSResize - RP internal toggle: enable-agentpool-vmsize-resize Changes: - agentpool_decorator.py: add update_vm_size() for VMSS pools and call it in update_agentpool_profile_preview() - _params.py: mark --node-vm-size as is_preview for nodepool update - _help.py: update help text and add VMSS resize example - test_agentpool_decorator.py: add unit tests for update_vm_size

Address review comments: 1. Remove the InvalidArgumentValueError in update_auto_scaler_properties() that blocked --node-vm-size for VMSS pools. This check was added when --node-vm-size only supported VirtualMachines pools, but now VMSS pools support VM size resize via rolling upgrade. 2. Add test case for VirtualMachines pool to verify update_vm_size() is a no-op (VMs pools handle VM size via the autoscaler update path). 3. Add HISTORY.rst entry for the new feature.

Add a live scenario test that creates a cluster with Standard_D2s_v3 and resizes the nodepool to Standard_D4s_v3 via `az aks nodepool update --node-vm-size`, verifying the rolling upgrade completes successfully. Addresses reviewer request for scenario test coverage with custom header bypass for the AgentPoolVMSSResize feature flag. Signed-off-by: wenhug <50309350+wenhug@users.noreply.github.com>

The test_update_agentpool_profile_preview tests mock all update methods called by update_agentpool_profile_preview(). Adding update_vm_size() to the call chain requires updating these mocks and assertions. Signed-off-by: wenhug <50309350+wenhug@users.noreply.github.com>

The scenario test requires real Azure credentials and cannot run in CI's recording/playback mode. Add @live_only() decorator to skip it in CI while still allowing manual live test runs. Signed-off-by: wenhug <50309350+wenhug@users.noreply.github.com>

wenhug · 2026-04-07T23:20:25Z

@FumingZhang @yonzhan ,addressed conflicts

FumingZhang

lgtm

FumingZhang · 2026-04-08T01:10:08Z

src/aks-preview/azext_aks_preview/tests/latest/test_aks_commands.py

+    @AKSCustomResourceGroupPreparer(
+        random_name_length=17, name_prefix="clitest", location="centraluseuap"
+    )
+    def test_aks_nodepool_update_vmss_vm_size_resize(


Queued live test to validate the change.

The live test failed with the following error, the custom feature header is not working?

raise HttpResponseError(response=response, model=error, error_format=ARMErrorFormat)

E azure.core.exceptions.HttpResponseError: (PropertyChangeNotAllowed) Changing property 'properties.vmSize' is not allowed.
E Code: PropertyChangeNotAllowed
E Message: Changing property 'properties.vmSize' is not allowed.
E Target: properties.vmSize

what is the test env, the RP code has not release to production yet

Has it reached to staging or EUAP? Queued test against EUAP. Just want to make sure the change works as expected.

The RP now gates VMSize resize by preview API version instead of AFEC feature registration, so the AKSHTTPCustomFeatures header is no longer needed. Signed-off-by: wenhug <50309350+wenhug@users.noreply.github.com>

Copilot AI review requested due to automatic review settings March 26, 2026 21:14

wenhug requested review from FumingZhang and andyliuliming as code owners March 26, 2026 21:14

azure-client-tools-bot-prd bot added this to the April 2026 (2026-04-07) milestone Mar 26, 2026

microsoft-github-policy-service bot requested review from yanzhudd, yonzhan and zhoxing-ms March 26, 2026 21:14

microsoft-github-policy-service bot assigned yanzhudd and zhoxing-ms Mar 26, 2026

microsoft-github-policy-service bot added Auto-Assign Auto assign by bot AKS labels Mar 26, 2026

Copilot started reviewing on behalf of wenhug March 26, 2026 21:16 View session

Copilot AI reviewed Mar 26, 2026

View reviewed changes

src/aks-preview/azext_aks_preview/agentpool_decorator.py Show resolved Hide resolved

src/aks-preview/azext_aks_preview/tests/latest/test_agentpool_decorator.py Show resolved Hide resolved

yonzhan unassigned zhoxing-ms Mar 26, 2026

FumingZhang reviewed Mar 27, 2026

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src/aks-preview/HISTORY.rst Show resolved Hide resolved

Wen Huang and others added 3 commits April 7, 2026 21:19

wenhug force-pushed the wenhuang/agentpool-vmsize-resize branch from 2f7b0ad to e51f6fa Compare April 7, 2026 21:21

FumingZhang reviewed Apr 8, 2026

View reviewed changes

fix: remove custom header from VMSS resize scenario test

c9bab47

The RP now gates VMSize resize by preview API version instead of AFEC feature registration, so the AKSHTTPCustomFeatures header is no longer needed. Signed-off-by: wenhug <50309350+wenhug@users.noreply.github.com>

Conversation

wenhug commented Mar 26, 2026

Summary

Usage

RP-side validation

Changes

Test plan

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Module: aks-preview

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