KubeVirt Scheduler¶
Scheduling is the process of matching Pods/VMs to Nodes. By default, the scheduler used is kube-scheduler. Further details can be found at Kubernetes Scheduler Documentation.
Custom schedulers can be used if the default scheduler does not satisfy your needs. For instance, you might want to schedule VMs using a load aware scheduler such as Trimaran Schedulers.
Creating a Custom Scheduler¶
KubeVirt is compatible with custom schedulers. The configuration steps are described in the Official Kubernetes Documentation. Please note, the Kubernetes version KubeVirt is running on and the Kubernetes version used to build the custom scheduler have to match. To get the Kubernetes version KubeVirt is running on, you can run the following command:
$ kubectl version
Client Version: version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.13", GitCommit:"a43c0904d0de10f92aa3956c74489c45e6453d6e", GitTreeState:"clean", BuildDate:"2022-08-17T18:28:56Z", GoVersion:"go1.16.15", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.13", GitCommit:"a43c0904d0de10f92aa3956c74489c45e6453d6e", GitTreeState:"clean", BuildDate:"2022-08-17T18:23:45Z", GoVersion:"go1.16.15", Compiler:"gc", Platform:"linux/amd64"}
Pay attention to the Server
line.
In this case, the Kubernetes version is v1.22.13
.
You have to checkout the matching Kubernetes version and build the Kubernetes project:
Then, you can follow the configuration steps described here.
Additionally, the ClusterRole system:kube-scheduler
needs permissions to use the verbs watch
, list
and get
on StorageClasses.
Scheduling VMs with the Custom Scheduler¶
The second scheduler should be up and running. You can check it with:
The deployment my-scheduler
should be up and running if everything is setup properly.
In order to launch the VM using the custom scheduler, you need to set the SchedulerName
in the VM's spec to my-scheduler
.
Here is an example VM definition:
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
name: vm-fedora
spec:
running: true
template:
spec:
schedulerName: my-scheduler
domain:
devices:
disks:
- name: containerdisk
disk:
bus: virtio
- name: cloudinitdisk
disk:
bus: virtio
rng: {}
resources:
requests:
memory: 1Gi
terminationGracePeriodSeconds: 180
volumes:
- containerDisk:
image: quay.io/containerdisks/fedora:latest
name: containerdisk
- cloudInitNoCloud:
userData: |-
#cloud-config
chpasswd:
expire: false
password: fedora
user: fedora
name: cloudinitdisk
SchedulerName
does not match any existing scheduler, the virt-launcher
pod will stay in state
Pending,
until the specified scheduler can be found.
You can check if the VM has been scheduled using the my-scheduler
checking the virt-launcher
pod events associated
with the VM. The pod should have been scheduled with my-scheduler
.
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
virt-launcher-vm-fedora-dpc87 2/2 Running 0 24m
$ kubectl describe pod virt-launcher-vm-fedora-dpc87
[...]
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 21m my-scheduler Successfully assigned default/virt-launcher-vm-fedora-dpc87 to node01
[...]