Extending Kubernetes Scheduler

Since SIF images do not support multiarch builds, its arch should be respected properly when it comes to pod scheduling. There are two options to make sure your SIF-based pod is scheduled on the node with a matching architecture: using nodeSelector in pod spec or configuring arch-scheduler extender.

This document will guide you through the second approach. To extend Kubernetes with arch extender the following steps are needed:

  1. launch arch-scheduler pod
  2. modify Kubernetes scheduler config
  3. restart Kubernetes scheduler

Launch arch-scheduler pod

Clone arch-scheduler repo:

$ git clone https://github.com/sylabs/arch-scheduler

Launch arch-scheduler pod:

$ cd arch-scheduler && \
  kubectl apply -f deploy/extender.yaml

This will make arch-scheduler run on the same node where default Kubernetes scheduler is located. Location of arch-scheduler is important since later Kubernetes scheduler will query it on localhost.

Modify Kubernetes scheduler config

This step requires changing current scheduler policy to include arch-scheduler extender in extenders list.

If you have already modified scheduler policy you probably know how to do that. Further assumed default scheduler has not been altered and arch-scheduler extender is the first change applied.

Copy config and policy files under default Kubernetes directory:

$ sudo mkdir /etc/kubernetes/scheduler && \
  sudo cp deploy/config.yaml /etc/kubernetes/scheduler && \
  sudo cp deploy/policy.yaml /etc/kubernetes/scheduler

Modify kube-scheduler pod:

$ sudo cp deploy/scheduler.yaml /etc/kubernetes/manifests/kube-scheduler.yaml


/etc/kubernetes/manifests/kube-scheduler.yaml is the default location of scheduler pod specification. If you changed that, make sure to update to the appropriate one.

Restart kube-scheduler pod

By default, Kubernetes watches for any changes on static pods, and default scheduler is one of them. This means right after you updated kube-scheduler pod changes should automatically be applied in some reasonable amount of time. In the end you should see all system pods running without any issues:

$ kubectl get po --namespace=kube-system

However, if kube-scheduler is not in a Running state, try to simply delete it and let Kubernetes recreate it once again correctly:

$ kubectl delete po --namespace=kube-system kube-scheduler


Kube-scheduler pod name may vary, make sure you are using correct one when deleting pod.