• bprashanth
  • enisoc
  • erictune
  • foxish
  • janetkuo
  • kow3ns
  • smarterclayton title: Scaling a StatefulSet

{% capture overview %} This page shows how to scale a StatefulSet. {% endcapture %}

{% capture prerequisites %}

  • StatefulSets are only available in Kubernetes version 1.5 or later.
  • Not all stateful applications scale nicely. You need to understand your StatefulSets well before continuing. If you're unsure, remember that it might not be safe to scale your StatefulSets.
  • You should perform scaling only when you're sure that your stateful application cluster is completely healthy.

{% endcapture %}

{% capture steps %}

Use kubectl to scale StatefulSets

Make sure you have kubectl upgraded to Kubernetes version 1.5 or later before continuing. If you're unsure, run kubectl version and check Client Version for which kubectl you're using.

kubectl scale

First, find the StatefulSet you want to scale. Remember, you need to first understand if you can scale it or not.

kubectl get statefulsets <stateful-set-name>

Change the number of replicas of your StatefulSet:

kubectl scale statefulsets <stateful-set-name> --replicas=<new-replicas>

Alternative: kubectl apply / kubectl edit / kubectl patch

Alternatively, you can do in-place updates on your StatefulSets.

If your StatefulSet was initially created with kubectl apply or kubectl create --save-config, update .spec.replicas of the StatefulSet manifests, and then do a kubectl apply:

kubectl apply -f <stateful-set-file-updated>

Otherwise, edit that field with kubectl edit:

kubectl edit statefulsets <stateful-set-name>

Or use kubectl patch:

kubectl patch statefulsets <stateful-set-name> -p '{"spec":{"replicas":<new-replicas>}}'


Scaling down doesn't not work right

You cannot scale down a StatefulSet when any of the stateful Pods it manages is unhealthy. Scaling down only takes place after those stateful Pods become running and ready.

With a StatefulSet of size > 1, if there is an unhealthy Pod, there is no way for Kubernetes to know (yet) if it is due to a permanent fault or a transient one (upgrade/maintenance/node reboot). If the Pod is unhealthy due to a permanent fault, scaling without correcting the fault may lead to a state where the StatefulSet membership drops below a certain minimum number of "replicas" that are needed to function correctly. This may cause your StatefulSet to become unavailable.

If the Pod is unhealthy due to a transient fault and the Pod might become available again, the transient error may interfere with your scale-up/scale-down operation. Some distributed databases have issues when nodes join and leave at the same time. It is better to reason about scaling operations at the application level in these cases, and perform scaling only when you're sure that your stateful application cluster is completely healthy.

{% endcapture %}

{% capture whatsnext %}

Learn more about deleting a StatefulSet.

{% endcapture %}

{% include templates/task.md %}