Need to upgrade AKS version to latest from 1.26.6. But its showing One or more node pools in the cluster are using a Kubernetes version that is 3 or more minor versions apart from the selected version. Upgrade control plane only is disabled. But while che

Question

Need to upgrade AKS version to latest from 1.26.6. But its showing One or more node pools in the cluster are using a Kubernetes version that is 3 or more minor versions apart from the selected version. Upgrade control plane only is disabled. But while checking to upgrade the node pool, its showing This node pool is using the latest version of Kubernetes supported by the cluster. To upgrade to a later version of Kubernetes, upgrade the cluster control plane first in the cluster configuration.

Answer 1

It is no longer possible to upgrade the control plane only. If a node pool’s version is more than two minor versions behind the control plane, or if it’s ahead of the control plane version, upgrades will be blocked.

My recommendation would be to use the CLI to create a new node pool with the supported version.

See: https://learn.microsoft.com/en-us/answers/questions/1624767/aks-cluster-upgrade-from-1-23-x-to-1-27-xFor that reason, to avoid AKS be in the EOL or Out of support, we have the option to auto upgrade or to keep updated your environment.

See: https://learn.microsoft.com/en-us/azure/aks/create-node-pools https://kubernetes.io/docs/reference/kubectl/generated/kubectl_cordon/

https://learn.microsoft.com/en-us/troubleshoot/azure/azure-kubernetes/create-upgrade-delete/nodepoolmcversionincompatible-error

You can mark it 'Accept Answer' and 'Upvote' if this helped you

Regards,

Abiola

Answer 2

Hi Adarsh P J,
Even though both control plane and node pool are on v1.26.6, when you try to upgrade the control plane to v1.30.x, Azure throws:

"One or more node pools in the cluster are using an older version of Kubernetes. Upgrade those node pools to version 1.28.x or greater before upgrading the cluster."

This means:

• Azure enforces version skew based on the target control plane version.
• Starting from Kubernetes v1.28, AKS allows node pools to be up to 3 versions behind the control plane, but this policy only applies after the control plane is v1.28 or higher.
• Your node pools are still v1.26.6, which is 4 versions behind the target. Hence, the control plane upgrade is blocked.

https://docs.azure.cn/en-us/aks/manage-node-pools

Will there be any issues due to the version mismatch between the control plane and the new node pool before the upgrade?
AFAIK, No major issues, if you upgrade the control plane immediately.

A node pool version can be up to two minor versions higher than the control plane version. This configuration is supported temporarily, such as for creating a new node pool and migrating workloads during an upgrade.
https://learn.microsoft.com/en-us/azure/aks/supported-kubernetes-versions?tabs=azure-cli#kubernetes-version-skew-support

Hope it helps!

Let me know if you have any further queries!

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Answer 3

Hi Adarsh P J

thank you for posting your question on the Q&A portal!

The error you’re seeing means there’s a big gap between the version of your control plane (the main part of the cluster) and the node pools (the worker nodes). AKS has a rule that you can’t have the control plane and node pools more than two minor versions apart. Since you’re trying to jump multiple versions at once, the system is blocking you for safety reasons.

Right now, your node pools are on a version that’s too far behind the latest one you want. That’s why the "Upgrade control plane only" option is disabled you need to bring your node pools closer first. But when you check the node pools, it says they’re already on the latest version supported by the current control plane. This is a bit confusing, but it means you need to upgrade the control plane first before the node pools can move further.

Here’s how to fix it step by step: First, upgrade your control plane to the next available version (like 1.27.x). Once that’s done, your node pools will then be allowed to upgrade to match or get closer to the control plane. After that, you can repeat the process until you reach the latest version.

You can find more details in the official Microsoft documentation on AKS upgrades here. It explains the version skew policy and how to safely upgrade.

Let me know if you get stuck at any point.

Best regards,
Alex
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