Migrate node image version to Azure Linux 3.0

Question

What is the rollback process if we need to revert after migrating to version 3.0?

If we run the following command to update the node pool:

az aks nodepool update \ --resource-group $RESOURCE_GROUP \ --cluster-name $CLUSTER_NAME \ --os-type Linux \ --os-sku AzureLinux3 \ --kubernetes-version 1.30.0 \ --name $NODE_POOL_NAME \ --node-count 1

Can we simply change the --os-sku parameter to AzureLinux2 and execute the command again to roll back?

I’ve checked the Microsoft documentation on upgrading OS versions but couldn’t find a direct answer.

How long will the upgrade process take for one node?

Answer 1

Please find answers to your queries asked earlier:

What is the rollback process if we need to revert after migrating to version 3.0? Can we simply change the --os-sku parameter to AzureLinux2 and execute the command again to roll back?

Yes you are almost right for the rollback process. You can use same command, but you'd be required to change --os-sku parameter to AzureLinux and that will pick the default OS version for the Kubernetes version your cluster is running onto.

see references: https://learn.microsoft.com/en-us/azure/aks/upgrade-os-version#roll-back-your-os-version-to-the-default-os-sku

How long will the upgrade process take for one node?

There isn’t a set timeframe for when a node will be upgraded to the new OS version, it depends on each cluster, so the timing can vary.

Roughly, an OS upgrade on the node will undergo these steps

drain -> reimage -> uncordon

And this also varies on various factors such as how much drain timeout, surge values, heavy/lightweight workloads, stateful/large data are there on the cluster. Thus, we won't be able to comment on the duration for the upgrade process.

Let me know if this clarifies your queries!!