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Chapter 6. Configuring schedulable control plane nodes

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In a high availability deployment, three or more nodes comprise the control plane. The control plane nodes are used for managing OpenShift Container Platform and for running the OpenShift containers. The remaining nodes are workers, used to run the customer containers and workloads. There can be anywhere between one to thousands of worker nodes.

For a single-node OpenShift cluster or for a cluster that comprises up to four nodes, the system automatically schedules the workloads to run on the control plane nodes.

For clusters of between five to ten nodes, you can choose to schedule workloads to run on the control plane nodes in addition to the worker nodes. This option is recommended for enhancing efficiency and preventing underutilized resources. You can select this option either during the installation setup, or as part of the post-installation steps.

For larger clusters of more than ten nodes, this option is not recommended.

This section explains how to schedule workloads to run on control plane nodes using the Assisted Installer web console and API, as part of the installation setup.

For instructions on how to configure schedulable control plane nodes following an installation, see Configuring control plane nodes as schedulable in the OpenShift Container Platform documentation.

Important

When you configure control plane nodes from the default unschedulable to schedulable, additional subscriptions are required. This is because control plane nodes then become worker nodes.

6.1. Configuring schedulable control planes using the web console

Prerequisites

  • You have set the cluster details.
  • You are installing OpenShift Container Platform 4.14 or later.

Procedure

  1. Log in to the Red Hat Hybrid Cloud Console and follow the instructions for installing OpenShift Container Platform using the Assisted Installer web console. For details, see Installing with the Assisted Installer web console in Additional Resources.
  2. When you reach the Host discovery page, click Add hosts.
  3. Optionally change the Provisioning type and additional settings as required. All options are compatible with schedulable control planes.
  4. Click Generate Discovery ISO to download the ISO.
  5. Set Run workloads on control plane nodes to on.

    Note

    For four nodes or less, this switch is activated automatically and cannot be changed.

  6. Click Next.

6.2. Configuring schedulable control planes using the API

Use the schedulable_masters attribute to enable workloads to run on control plane nodes.

Prerequisites

  • You have generated a valid API_TOKEN. Tokens expire every 15 minutes.
  • You have created a $PULL_SECRET variable.
  • You are installing OpenShift Container Platform 4.14 or later.

Procedure

  1. Follow the instructions for installing Assisted Installer using the Assisted Installer API. For details, see Installing with the Assisted Installer API in Additional Resources.
  2. When you reach the step for registering a new cluster, set the schedulable_masters attribute as follows:

    $ curl https://api.openshift.com/api/assisted-install/v2/clusters/${CLUSTER_ID} \
    -X PATCH \
    -H "Authorization: Bearer ${API_TOKEN}" \
    -H "Content-Type: application/json" \
    -d '
    {
      "schedulable_masters": true 1
    }
    ' | jq
    1
    Enables the scheduling of workloads on the control plane nodes.

6.3. Additional resources

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