Azure Kubernetes Service (AKS) node Image upgrade – Preview

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You may have read my previous blog post on applying OS updates to your Azure Kubernetes Cluster (AKS) without doing a cluster upgrade https://pixelrobots.co.uk/2019/05/apply-os-updates-to-aks-nodes-without-an-upgrade/. This method used kured (KUbernetes REboot Daemon) by weaveworks  https://github.com/weaveworks/kured. This method installed some Kubernetes resources onto your cluster. This new method, which is still in preview at the time this article was written does not install anything on to your cluster. The AKS OS images get updated once a week

Below I will go through the steps you need to follow to implement this new and improved method. Just remember, as this is in preview do not implement this on your production cluster just yet.

Register the preview feature

To start with as this is in preview you will need to register the preview feature. To do this you will use the az feature register command.

After several minutes, the registration will complete. To check that it has finished you can use the az feature list command.

You will also need to install the most up to date aks-preview cli extenstion. For this you will need to use the az extension add or az extension update commands.

As I have the latest updates, I get the message above.  If you get no message, then it would have updated.

Time to Upgrade all nodes in all node pools

For this you will be using the az aks upgrade command with the –node-image-only command.

To check on the progress of your upgrade you can use the following kubectl command.

As you can see one node has been up for 5 minutes and 46 seconds. That one has been updated. It’s now moving to the next ones. This can take some time. After a while you can use the following command to check the state of the cluster.

To check that the upgrade has finished you can use the az aks show command.

If it does not say succeeded, then it is still doing the upgrade.

And that’s it, you have upgraded the whole cluster to the latest OS image but wait there are more options!

Upgrade a specific node pool

For this I am going to use another cluster as the one I used above is all updated.

So, to upgrade just one node pool you use the az aks nodepool upgrade command.

I found in my tests that a nodepool upgrade sits showing running till it has finished. You could add –no-wait to this command, so you do not have to wait.

To check that the node pool has finished upgrading you can use the az aks nodepool show command.

All in All

I really like this new feature and would like to see a way to schedule it. Perhaps, an Azure logic app could do this by spinning up container in Azure Container Instances (ACI). You could also do this via a DevOps pipeline. I would ideally like to see a nice effortless way in the portal or via CLI.

If you have any thoughts let me know.

Thanks for reading, and if you have any comments or questions please reach out.