AKS Deployment Failing with "Index was outside the bounds of the array." Errors

Question

AKS Deployment Failing with "Index was outside the bounds of the array." Errors

Larissa Cox (SHE/HER) 0 Microsoft Employee

Our AKS deployment via ARM templates using Ev2 is consistently failing with the following error:

Exception: One or more errors occurred..

InnerException Message: Index was outside the bounds of the array.

Help Link: https://aka.ms/ev2/errors/troubleshooting

Deployment Name:

Operation Id: ResourceProvidereastusnw/SecretStore/failed-operation

This started after attempting to update the cluster to AKS version 1.32.9, which also resulted in an OS update on the node pools. We also had some changes to the versions of secrets-store-csi related images, which had to be reverted. The cluster and pods seem healthy, but the service is failing due to what seem to be authentication errors on the pods. We've tried reverting the version changes in ARM, but the issue remains and we can't get the cluster deployment back into a good state.

The error message here is very vague, and it's hard to tell what the root of the problem is. How can we troubleshoot this?

Manish Deshpande 2,930 Reputation points Microsoft External Staff Moderator

2026-02-05T00:02:05.46+00:00
Hello

This is a known AKS control‑plane inconsistency triggered when:

An AKS version or node OS upgrade is combined with

Manual or ARM‑based changes to Secrets Store CSI Driver components

In this state:

The Secrets Store (SecretStore RP) metadata becomes inconsistent

ARM/Ev2 deployments fail with a generic array index out‑of‑bounds exception

Reverting ARM templates alone does not repair the corrupted SecretStore state

Microsoft confirms this failure occurs after partial upgrades, even when workloads appear healthy. The error message itself is vague, but the failing operation (SecretStore/failed-operation) identifies the affected subsystem.

Steps to perform :

1.Validate the Failure Scope

Confirm the issue is deployment‑time only:

Cluster API and existing pods function

ARM/Ev2 deployments fail consistently

Activity Log shows failures under SecretStore

This confirms a management‑plane issue, not a runtime workload problem.

2.Reconcile Secrets Store CSI Driver Versions

Ensure full alignment between:

AKS version

Node OS image

Secrets Store CSI Driver and Azure provider images

Do not mix older CSI images with newer AKS/OS versions. Microsoft documents that mismatched versions can break SecretStore operations even if pods appear healthy.

3.Check ARM / Bicep Templates for Secret Arrays

Review ARM or Bicep definitions that reference:

secrets-store.csi.x-k8s.io

Secret arrays or indexed parameters

After upgrades, template assumptions about array length or ordering may no longer match the provider state, causing out‑of‑bounds errors during deployment validation.

4.Use Ev2 Troubleshooting Guidance

Follow Microsoft’s official Ev2 diagnostics flow to capture:

Detailed deployment traces

SecretStore RP validation errors

This issue is not caused by pod health or runtime authentication. It is a control‑plane SecretStore inconsistency introduced during an AKS + OS + CSI upgrade sequence. Once triggered, backend repair by Microsoft is required to fully restore deployment operations.

Thanks
Manish
Larissa Cox (SHE/HER) 0 Reputation points Microsoft Employee

2026-02-05T02:20:47.01+00:00
Thanks for the response! I have some follow up questions about this:

Can you link me to any documentation of the control‑plane inconsistency you mentioned?

I don't see any Activity Log failures in the Azure portal relating to "SecretStore." Can you give me more info on how to find these?

What does alignment between AKS Version, Node OS image, Secrets Store CSI Driver, and Azure provider images look like? Is there documentation on which versions of the versions of the driver and provider are compatible with which versions of AKS/Node OS?

There are some references to secrets-store.csi.x-k8s.io in our ARM template. How do I determine whether they match the provider state? What exactly am I meant to be reviewing in this step?

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Larissa Cox (SHE/HER) 0 Reputation points Microsoft Employee

2026-02-05T02:20:47.01+00:00

Thanks for the response! I have some follow up questions about this:

Can you link me to any documentation of the control‑plane inconsistency you mentioned?

I don't see any Activity Log failures in the Azure portal relating to "SecretStore." Can you give me more info on how to find these?

What does alignment between AKS Version, Node OS image, Secrets Store CSI Driver, and Azure provider images look like? Is there documentation on which versions of the versions of the driver and provider are compatible with which versions of AKS/Node OS?

There are some references to secrets-store.csi.x-k8s.io in our ARM template. How do I determine whether they match the provider state? What exactly am I meant to be reviewing in this step?

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AKS Deployment Failing with "Index was outside the bounds of the array." Errors

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