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

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

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

❌Azure CLI Extensions Breaking Change Test

❌managedcleanroom

rule cmd_name rule_message suggest_message

❌ 1006 - ParaAdd managedcleanroom collaboration add-collaborator cmd managedcleanroom collaboration add-collaborator added parameter email please remove parameter email for cmd managedcleanroom collaboration add-collaborator

❌ 1007 - ParaRemove managedcleanroom collaboration add-collaborator cmd managedcleanroom collaboration add-collaborator removed parameter object_id please add back parameter object_id for cmd managedcleanroom collaboration add-collaborator

❌ 1007 - ParaRemove managedcleanroom collaboration add-collaborator cmd managedcleanroom collaboration add-collaborator removed parameter tenant_id please add back parameter tenant_id for cmd managedcleanroom collaboration add-collaborator

❌ 1007 - ParaRemove managedcleanroom collaboration add-collaborator cmd managedcleanroom collaboration add-collaborator removed parameter user_identifier please add back parameter user_identifier for cmd managedcleanroom collaboration add-collaborator

❌ 1006 - ParaAdd managedcleanroom collaboration create cmd managedcleanroom collaboration create added parameter consortium_type please remove parameter consortium_type for cmd managedcleanroom collaboration create

❌ 1006 - ParaAdd managedcleanroom collaboration create cmd managedcleanroom collaboration create added parameter user_identity please remove parameter user_identity for cmd managedcleanroom collaboration create

❌ 1007 - ParaRemove managedcleanroom collaboration create cmd managedcleanroom collaboration create removed parameter collaborators please add back parameter collaborators for cmd managedcleanroom collaboration create

⚠️ 1006 - ParaAdd managedcleanroom collaboration update cmd managedcleanroom collaboration update added parameter consortium_type

⚠️ 1006 - ParaAdd managedcleanroom collaboration update cmd managedcleanroom collaboration update added parameter user_identity

⚠️ 1006 - ParaAdd managedcleanroom consortium create cmd managedcleanroom consortium create added parameter consortium_type

⚠️ 1006 - ParaAdd managedcleanroom consortium update cmd managedcleanroom consortium update added parameter consortium_type

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 19.0.0b29 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()`.

Copilot · 2026-03-26T21:21:50Z

src/aks-preview/azext_aks_preview/agentpool_decorator.py

+        # Skip for VirtualMachines pools - they handle VM size via autoscaler path
+        if self.context.get_vm_set_type() == CONST_VIRTUAL_MACHINES:
+            return agentpool
+
+        node_vm_size = self.context.raw_param.get("node_vm_size")
+        if node_vm_size:
+            agentpool.vm_size = node_vm_size


update_auto_scaler_properties() in this same decorator still raises InvalidArgumentValueError whenever raw_param['node_vm_size'] is not None for VMSS pools ("Updating VM size is not supported for virtual machine scale set agentpools."). With VMSS resize now supported via --node-vm-size, this guard will block the new behavior if update_auto_scaler_properties() is invoked as part of the update flow (e.g., by the default update profile). Consider removing or narrowing that validation so VMSS pools can accept --node-vm-size without throwing.

Suggested change

# Skip for VirtualMachines pools - they handle VM size via autoscaler path

if self.context.get_vm_set_type() == CONST_VIRTUAL_MACHINES:

return agentpool

node_vm_size = self.context.raw_param.get("node_vm_size")

if node_vm_size:

agentpool.vm_size = node_vm_size

vm_set_type = self.context.get_vm_set_type()

# Skip for VirtualMachines pools - they handle VM size via autoscaler path

if vm_set_type == CONST_VIRTUAL_MACHINES:

return agentpool

# Only apply direct VM size changes for VMSS pools

if vm_set_type == CONST_VIRTUAL_MACHINE_SCALE_SETS:

node_vm_size = self.context.raw_param.get("node_vm_size")

if node_vm_size:

# Apply the new VM size to the agent pool

agentpool.vm_size = node_vm_size

# Clear the raw_param value so downstream autoscaler validation

# (which still checks node_vm_size for VMSS) does not reject

# this supported VM size update.

self.context.raw_param["node_vm_size"] = None

Copilot · 2026-03-26T21:21:50Z

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

+            vm_size="Standard_D4s_v3"
+        )
+        self.assertEqual(dec_agentpool_2, ground_truth_agentpool_2)
+


The new unit tests cover VMSS behavior, but they don't cover the VirtualMachines pool branch where update_vm_size() should be a no-op (VM size changes are handled via the autoscaler update path). Add a test case with type=CONST_VIRTUAL_MACHINES and node_vm_size set to ensure update_vm_size() does not mutate agentpool.vm_size for VMs pools.

Suggested change

# Test case 3: VirtualMachines pool with node_vm_size provided (should be no-op)

dec_3 = AKSPreviewAgentPoolUpdateDecorator(

self.cmd,

self.client,

{"node_vm_size": "Standard_D4s_v3"},

self.resource_type,

self.agentpool_decorator_mode,

)

agentpool_3 = self.create_initialized_agentpool_instance(

vm_size="Standard_D2s_v3"

)

# For VirtualMachines pools, update_vm_size should be a no-op; VM size changes are

# handled via the autoscaler update path.

agentpool_3.type = CONST_VIRTUAL_MACHINES

dec_3.context.attach_agentpool(agentpool_3)

dec_agentpool_3 = dec_3.update_vm_size(agentpool_3)

ground_truth_agentpool_3 = self.create_initialized_agentpool_instance(

vm_size="Standard_D2s_v3"

)

ground_truth_agentpool_3.type = CONST_VIRTUAL_MACHINES

self.assertEqual(dec_agentpool_3, ground_truth_agentpool_3)

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.

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

FumingZhang · 2026-03-27T02:58:37Z

src/aks-preview/HISTORY.rst


 Pending
 +++++++
+* `az aks nodepool update`: Support `--node-vm-size` to resize VM size of an existing VMSS-based agent pool (preview). Requires AFEC registration `Microsoft.ContainerService/AgentPoolVMSSResize`.


Is it possible to bypass the feature flag validation via custom header? If so, please add a scenario test to ensure the change works as expected.

FumingZhang · 2026-03-30T03:49:37Z

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

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

yonzhan unassigned zhoxing-ms Mar 26, 2026

FumingZhang reviewed Mar 27, 2026

View reviewed changes

+        # Test case 3: VirtualMachines pool with node_vm_size provided (should be no-op)
+        dec_3 = AKSPreviewAgentPoolUpdateDecorator(
+            self.cmd,
+            self.client,
+            {"node_vm_size": "Standard_D4s_v3"},
+            self.resource_type,
+            self.agentpool_decorator_mode,
+        )
+        agentpool_3 = self.create_initialized_agentpool_instance(
+            vm_size="Standard_D2s_v3"
+        )
+        # For VirtualMachines pools, update_vm_size should be a no-op; VM size changes are
+        # handled via the autoscaler update path.
+        agentpool_3.type = CONST_VIRTUAL_MACHINES
+        dec_3.context.attach_agentpool(agentpool_3)
+        dec_agentpool_3 = dec_3.update_vm_size(agentpool_3)
+        ground_truth_agentpool_3 = self.create_initialized_agentpool_instance(
+            vm_size="Standard_D2s_v3"
+        )
+        ground_truth_agentpool_3.type = CONST_VIRTUAL_MACHINES
+        self.assertEqual(dec_agentpool_3, ground_truth_agentpool_3)

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wenhug commented Mar 26, 2026

Summary

Usage

RP-side validation

Changes

Test plan

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