--- title: Scheduling pods using a secondary scheduler --- # Scheduling pods using a secondary scheduler {#secondary-scheduler-configuring} You can run a custom secondary scheduler in OpenShift Container Platform by installing the Secondary Scheduler Operator, deploying the secondary scheduler, and setting the secondary scheduler in the pod definition. ## Installing the Secondary Scheduler Operator {#nodes-secondary-scheduler-install-console_secondary-scheduler-configuring} You can install the Secondary Scheduler Operator for Red Hat OpenShift through the OpenShift Container Platform web console to configure a secondary scheduler. **Prerequisites** - You are logged in to OpenShift Container Platform as a user with the `cluster-admin` role. - You have 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 Secondary Scheduler Operator for Red Hat OpenShift. 1. Navigate to **Administration** → **Namespaces** and click **Create Namespace**. 2. Enter `openshift-secondary-scheduler-operator` in the **Name** field and click **Create**. 3. Install the Secondary Scheduler Operator for Red Hat OpenShift. 1. Navigate to **Ecosystem** → **Software Catalog**. 2. Enter **Secondary Scheduler Operator for Red Hat OpenShift** into the filter box. 3. Select the **Secondary Scheduler Operator for Red Hat OpenShift** and click **Install**. 4. On the **Install Operator** page: 1. The **Update channel** is set to **stable**, which installs the latest stable release of the Secondary Scheduler Operator for Red Hat OpenShift. 2. Select **A specific namespace on the cluster** and select **openshift-secondary-scheduler-operator** from the drop-down menu. 3. Select an **Update approval** strategy. - The **Automatic** strategy allows Operator Lifecycle Manager (OLM) to automatically update the Operator when a new version is available. - The **Manual** strategy requires a user with appropriate credentials to approve the Operator update. 4. Click **Install**. **Verification** 1. Navigate to **Ecosystem** → **Installed Operators**. 2. Verify that **Secondary Scheduler Operator for Red Hat OpenShift** is listed with a **Status** of **Succeeded**. ## Deploying a secondary scheduler {#nodes-secondary-scheduler-configuring-console_secondary-scheduler-configuring} After you have installed the Secondary Scheduler Operator, you can deploy a secondary scheduler to apply custom placement logic for specific pods. **Prerequisites** - You are logged in to OpenShift Container Platform as a user with the `cluster-admin` role. - You have access to the OpenShift Container Platform web console. - The Secondary Scheduler Operator for Red Hat OpenShift is installed. **Procedure** 1. Log in to the OpenShift Container Platform web console. 2. Create config map to hold the configuration for the secondary scheduler. 1. Navigate to **Workloads** → **ConfigMaps**. 2. Click **Create ConfigMap**. 3. In the YAML editor, enter the config map definition that contains the necessary `KubeSchedulerConfiguration` configuration. For example: ```yaml apiVersion: v1 kind: ConfigMap metadata: name: "secondary-scheduler-config" namespace: "openshift-secondary-scheduler-operator" data: "config.yaml": | apiVersion: kubescheduler.config.k8s.io/v1 kind: KubeSchedulerConfiguration leaderElection: leaderElect: false profiles: - schedulerName: secondary-scheduler plugins: score: disabled: - name: NodeResourcesBalancedAllocation - name: NodeResourcesLeastAllocated ``` where: `metadata.name` : Specifies the name of the config map. This is used in the **Scheduler Config** field when creating the `SecondaryScheduler` CR. `metadata.namespace` : Specifies the namespace to create the config map in. The namespace must be `openshift-secondary-scheduler-operator`. `data."config.yaml".kind` : Specifies the `KubeSchedulerConfiguration` resource for the secondary scheduler. For more information, see [`KubeSchedulerConfiguration`](https://kubernetes.io/docs/reference/config-api/kube-scheduler-config.v1/#kubescheduler-config-k8s-io-v1-KubeSchedulerConfiguration) in the Kubernetes API documentation. `data."config.yaml".profiles.schedulerName` : Specifies the name of the secondary scheduler. Pods that set their `spec.schedulerName` field to this value are scheduled with this secondary scheduler. `data."config.yaml".profiles.plugins` : Specifies the plugins to enable or disable for the secondary scheduler. For a list default scheduling plugins, see [Scheduling plugins](https://kubernetes.io/docs/reference/scheduling/config/#scheduling-plugins) in the Kubernetes documentation. 4. Click **Create**. 3. Create the `SecondaryScheduler` CR: 1. Navigate to **Ecosystem** → **Installed Operators**. 2. Select **Secondary Scheduler Operator for Red Hat OpenShift**. 3. Select the **Secondary Scheduler** tab and click **Create SecondaryScheduler**. 4. The **Name** field defaults to `cluster`; do not change this name. 5. The **schedulerConfig** field defaults to `secondary-scheduler-config`. Ensure that this value matches the name of the config map created earlier in this procedure. 6. In the **schedulerImage** field, enter the image name for your custom scheduler. > [!IMPORTANT] > Red Hat does not directly support the functionality of your custom secondary scheduler. 7. Optional: To enable high availability for the secondary scheduler, configure the following settings: 1. Expand the **topology** section. 2. In the **mode** field, select **HighlyAvailable**. 3. In the **maxReplicas** field, enter the maximum number of secondary scheduler replicas to deploy. If unset, the maximum number of replicas is `3`. 4. In the **tolerations** field, enter tolerations to allow scheduler replicas on tainted nodes. If unset, no taints are tolerated. > [!NOTE] > To configure node selectors, use the **YAML view** option. Add the `spec.topology.highlyAvailableTopology.nodeSelector` field and enter the necessary node labels to target a specific group of nodes for scheduler replica placement. If unset, all nodes are considered. 8. Click **Create**. ## Scheduling a pod using the secondary scheduler {#nodes-secondary-scheduler-pod-console_secondary-scheduler-configuring} To schedule a pod by using the secondary scheduler, set the `schedulerName` field in the pod definition. **Prerequisites** - You are logged in to OpenShift Container Platform as a user with the `cluster-admin` role. - You have access to the OpenShift Container Platform web console. - The Secondary Scheduler Operator for Red Hat OpenShift is installed. - A secondary scheduler is configured. **Procedure** 1. Log in to the OpenShift Container Platform web console. 2. Navigate to **Workloads** → **Pods**. 3. Click **Create Pod**. 4. In the YAML editor, enter the desired pod configuration and add the `schedulerName` field: ```yaml apiVersion: v1 kind: Pod metadata: name: nginx namespace: default spec: securityContext: runAsNonRoot: true seccompProfile: type: RuntimeDefault containers: - name: nginx image: nginx:1.14.2 ports: - containerPort: 80 securityContext: allowPrivilegeEscalation: false capabilities: drop: [ALL] schedulerName: secondary-scheduler ``` The `spec.schedulerName` field must match the name that is defined in the config map when you configured the secondary scheduler. 5. Click **Create**. **Verification** 1. Log in to the OpenShift CLI. 2. Describe the pod using the following command: ```terminal $ oc describe pod nginx -n default ``` ```text {title="Example output"} Name: nginx Namespace: default Priority: 0 Node: ci-ln-t0w4r1k-72292-xkqs4-worker-b-xqkxp/10.0.128.3 ... Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Scheduled 12s secondary-scheduler Successfully assigned default/nginx to ci-ln-t0w4r1k-72292-xkqs4-worker-b-xqkxp ... ``` 3. In the events table, find the event with a message similar to `Successfully assigned / to `. 4. In the "From" column, verify that the event was generated from the secondary scheduler and not the default scheduler. > [!NOTE] > You can also check the `secondary-scheduler-*` pod logs in the `openshift-secondary-scheduler-namespace` to verify that the pod was scheduled by the secondary scheduler.