--- title: Enabling descheduler evictions on virtual machines --- # Enabling descheduler evictions on virtual machines {#virt-enabling-descheduler-evictions} You can use the descheduler to evict pods so that the pods can be rescheduled onto more appropriate nodes. If the pod is a virtual machine, the pod eviction causes the virtual machine to be live migrated to another node. ## Descheduler profiles {#nodes-descheduler-profiles_virt-enabling-descheduler-evictions} Use descheduler profiles to enable specific eviction strategies that rebalance your cluster based on criteria such as pod lifecycle or node utilization. Use the `KubeVirtRelieveAndMigrate` profile to enable the descheduler on a virtual machine. `KubeVirtRelieveAndMigrate` : The `KubeVirtRelieveAndMigrate` profile evicts pods from high-cost nodes to reduce overall resource expenses and enable workload migration. It also periodically rebalances workloads to help maintain similar spare capacity across nodes, which supports better handling of sudden workload spikes. Nodes can experience the following costs: - **Resource utilization**: Increased resource pressure raises the overhead for running applications. - **Node maintenance**: A higher number of containers on a node increases resource consumption and maintenance costs. The profile enables the `LowNodeUtilization` strategy with the alpha-level `EvictionsInBackground` feature. By default, the profile uses the `PrometheusCPUMemoryCombinedProfile` utilization metric. This metric combines CPU and memory utilization with pressure stall information (PSI) for both dimensions for comprehensive node load balancing. The profile also exposes the following customization fields: - `devActualUtilizationProfile`: Enables load-aware descheduling. You can configure the following utilization profiles: - `PrometheusCPUMemoryCombinedProfile` (default): Balances nodes based on CPU utilization, CPU PSI pressure, memory utilization, and memory PSI pressure. This profile is ideal for environments with memory overcommit enabled, as it spreads the load and prevents resource contention. - `PrometheusCPUCombined`: Balances nodes based on CPU utilization and CPU PSI pressure only. Use this profile in environments without memory overcommit, where memory allocations are strictly guaranteed and CPU pressure is the primary driver for workload distribution. - `devLowNodeUtilizationThresholds`: Sets experimental thresholds for the `LowNodeUtilization` strategy. Do not use this field with `devDeviationThresholds`. - `devDeviationThresholds`: Treats nodes with below-average resource usage as underutilized to help redistribute workloads from overutilized nodes. Do not use this field with `devLowNodeUtilizationThresholds`. Supported values are: `Low` (10%:10%), `Medium` (20%:20%), `High` (30%:30%), `AsymmetricLow` (0%:10%), `AsymmetricMedium` (0%:20%), `AsymmetricHigh` (0%:30%). - `devEnableSoftTainter`: Enables the soft-tainting component to dynamically apply or remove soft taints as scheduling hints. Example configuration: ```yaml apiVersion: operator.openshift.io/v1 kind: KubeDescheduler metadata: name: cluster namespace: openshift-kube-descheduler-operator spec: managementState: Managed deschedulingIntervalSeconds: 30 mode: "Automatic" profiles: - KubeVirtRelieveAndMigrate profileCustomizations: devEnableSoftTainter: true devDeviationThresholds: AsymmetricLow devActualUtilizationProfile: PrometheusCPUMemoryCombinedProfile ``` The `KubeVirtRelieveAndMigrate` profile requires PSI metrics to be enabled on all worker nodes. You can enable this by applying the following `MachineConfig` custom resource (CR): Example `MachineConfig` CR: ```yaml apiVersion: machineconfiguration.openshift.io/v1 kind: MachineConfig metadata: labels: machineconfiguration.openshift.io/role: worker name: 99-openshift-machineconfig-worker-psi-karg spec: kernelArguments: - psi=1 ``` > [!NOTE] > The name of the `MachineConfig` object is significant because machine configs are processed in lexicographical order. By default, a config that starts with `98-` disables PSI. To ensure that PSI is enabled, name your config with a higher prefix, such as `99-openshift-machineconfig-worker-psi-karg`. You can use this profile with the `SoftTopologyAndDuplicates` profile to also rebalance pods based on soft topology constraints, which can be useful in hosted control plane environments. ## Installing the descheduler {#nodes-descheduler-installing_virt-enabling-descheduler-evictions} The descheduler is not available by default. To enable the descheduler, you must install the Kube Descheduler Operator from the software catalog and enable one or more descheduler profiles. By default, the descheduler runs in predictive mode, which means that it only simulates pod evictions. You must change the mode to automatic for the descheduler to perform the pod evictions. > [!IMPORTANT] > If you have enabled hosted control planes in your cluster, set a custom priority threshold to lower the chance that pods in the hosted control plane namespaces are evicted. Set the priority threshold class name to `hypershift-control-plane`, because it has the lowest priority value (`100000000`) of the hosted control plane priority classes. **Prerequisites** - You are logged in to OpenShift Container Platform as a user with the `cluster-admin` role. - Access to the OpenShift Container Platform web console. **Procedure** 1. Log in to the OpenShift Container Platform 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 **Ecosystem** → **Software Catalog**. 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 **Ecosystem** → **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. To evict pods instead of simulating the evictions, change the **Mode** field to **Automatic**. 2. Expand the **Profiles** section and select `KubeVirtRelieveAndMigrate`. The `AffinityAndTaints` profile is enabled by default. > [!NOTE] > You can also configure the profiles and settings for the descheduler later using the OpenShift CLI (`oc`). ## Configuring descheduler evictions for virtual machines {#virt-configuring-descheduler-evictions_virt-enabling-descheduler-evictions} After the descheduler is installed and configured, all migratable virtual machines (VMs) are eligible for eviction by default. You can configure the descheduler to manage VM evictions across the cluster and optionally exclude specific VMs from eviction. **Prerequisites** - Install the descheduler in the OpenShift Container Platform web console or OpenShift CLI (`oc`). **Procedure** 1. Stop the VM. 2. Configure the `KubeDescheduler` object with the `KubeVirtRelieveAndMigrate` profile and enable background evictions for improved VM eviction stability during live migration: ```yaml apiVersion: operator.openshift.io/v1 kind: KubeDescheduler metadata: name: cluster namespace: openshift-kube-descheduler-operator spec: deschedulingIntervalSeconds: 60 profiles: - KubeVirtRelieveAndMigrate mode: Automatic ``` 3. Optional: To evict pods, set the `mode` field value to `Automatic`. By default, the descheduler does not evict pods. 4. Optional: Configure limits for the number of parallel evictions to improve stability in large clusters. The descheduler can limit the number of concurrent evictions per node and across the cluster by using the `evictionLimits` field. Set these limits to match the migration limits configured in the `HyperConverged` custom resource (CR). ```yaml spec: evictionLimits: node: 2 total: 5 ``` Set values that correspond to the migration limits in the `HyperConverged` CR: ```yaml spec: liveMigrationConfig: parallelMigrationsPerCluster: 5 parallelOutboundMigrationsPerNode: 2 ``` 5. Optional: To exclude the VM from eviction, add the `descheduler.alpha.kubernetes.io/prefer-no-eviction` annotation to the `spec.template.metadata.annotations` field. The change is applied dynamically and is propagated to the `VirtualMachineInstance` (VMI) object and the `virt-launcher` pod. Only the presence of the annotation is checked. The value is not evaluated, so `"true"` and `"false"` have the same effect. ```yaml apiVersion: kubevirt.io/v1 kind: VirtualMachine spec: template: metadata: annotations: descheduler.alpha.kubernetes.io/prefer-no-eviction: "true" ``` 6. Start the VM. **Result** The VM is now configured according to the descheduler settings. **Additional resources** {._additional-resources} - [Descheduler overview](/openshift-docs-markdown/nodes/scheduling/descheduler/index#nodes-descheduler-about)