Enabling descheduler evictions on virtual machines

The descheduler can be used to evict a running pod to allow the pod to be rescheduled onto a more suitable node. You must install the descheduler by using the OKD web console or OpenShift CLI (oc) before you can enable it on your virtual machine (VM).

Descheduler profiles

Use the Technology Preview DevPreviewLongLifecycle profile to enable the descheduler on a virtual machine. This is the only descheduler profile currently available for OKD Virtualization. To ensure proper scheduling, create VMs with CPU and memory requests for the expected load.

DevPreviewLongLifecycle

This profile balances resource usage between nodes and enables the following strategies:

• RemovePodsHavingTooManyRestarts: removes pods whose containers have been restarted too many times and pods where the sum of restarts over all containers (including Init Containers) is more than 100. Restarting the VM guest operating system does not increase this count.

• LowNodeUtilization: evicts pods from overutilized nodes when there are any underutilized nodes. The destination node for the evicted pod will be determined by the scheduler.

  • A node is considered underutilized if its usage is below 20% for all thresholds (CPU, memory, and number of pods).

  • A node is considered overutilized if its usage is above 50% for any of the thresholds (CPU, memory, and number of pods).

Installing the descheduler

The descheduler is not available by default. To enable the descheduler, you must install the Kube Descheduler Operator from OperatorHub and enable one or more descheduler profiles.

Prerequisites

• Cluster administrator privileges.

• Access to the OKD web console.

• Ensure that you have downloaded the pull secret from the Red Hat OpenShift Cluster Manager as shown in Obtaining the installation program in the installation documentation for your platform.

  If you have the pull secret, add the redhat-operators catalog to the OperatorHub custom resource (CR) as shown in Configuring OKD to use Red Hat Operators.

Procedure

1. Log in to the OKD web console.

2. Create the required namespace for the Kube Descheduler Operator.

   1. Navigate to Administration → Namespaces and click Create Namespace.

   2. Enter openshift-kube-descheduler-operator in the Name field, enter openshift.io/cluster-monitoring=true in the Labels field to enable descheduler metrics, and click Create.

3. Install the Kube Descheduler Operator.

   1. Navigate to Operators → OperatorHub.

   2. Type Kube Descheduler Operator into the filter box.

   3. Select the Kube Descheduler Operator and click Install.

   4. On the Install Operator page, select A specific namespace on the cluster. Select openshift-kube-descheduler-operator from the drop-down menu.

   5. Adjust the values for the Update Channel and Approval Strategy to the desired values.

   6. Click Install.

4. Create a descheduler instance.

   1. From the Operators → Installed Operators page, click the Kube Descheduler Operator.

   2. Select the Kube Descheduler tab and click Create KubeDescheduler.

   3. Edit the settings as necessary.

      1. Expand the Profiles section and select DevPreviewLongLifecycle. The AffinityAndTaints profile is enabled by default.

         The only profile currently available for OKD Virtualization is DevPreviewLongLifecycle.

You can also configure the profiles and settings for the descheduler later using the OpenShift CLI (oc).

Enabling descheduler evictions on a virtual machine (VM)

After the descheduler is installed, you can enable descheduler evictions on your VM by adding an annotation to the VirtualMachine custom resource (CR).

Prerequisites

• Install the descheduler in the OKD web console or OpenShift CLI (oc).

• Ensure that the VM is not running.

Procedure

1. Before starting the VM, add the descheduler.alpha.kubernetes.io/evict annotation to the VirtualMachine CR:

   apiVersion: kubevirt.io/v1
   kind: VirtualMachine
   spec:
     template:
       metadata:
         annotations:
           descheduler.alpha.kubernetes.io/evict: "true"

2. If you did not already set the DevPreviewLongLifecycle profile in the web console during installation, specify the DevPreviewLongLifecycle in the spec.profile section of the KubeDescheduler object:

   apiVersion: operator.openshift.io/v1
   kind: KubeDescheduler
   metadata:
     name: cluster
     namespace: openshift-kube-descheduler-operator
   spec:
     deschedulingIntervalSeconds: 3600
     profiles:
     - DevPreviewLongLifecycle

The descheduler is now enabled on the VM.