Node Selector

If you want to restrict Longhorn components to only run on a particular set of nodes, you can set node selector for all Longhorn components. For example, you want to install Longhorn in a cluster that has both Linux nodes and Windows nodes but Longhorn cannot run on Windows nodes. In this case, you can set the node selector to restrict Longhorn to only run on Linux nodes.

For more information about how node selector work, refer to the official Kubernetes documentation.

Setting up Node Selector for Longhorn

Longhorn system contains user deployed components (e.g, Manager, Driver Deployer, UI) and system managed components (e.g, Instance Manager, Engine Image, CSI Driver, etc.) You need to set node selector for both types of components. See more details below.

Setting up Node Selector During installing Longhorn

  1. Set node selector for user deployed components (Manager, UI, Driver Deployer)

    • If you install Longhorn by Rancher 2.5.x, you need to click Edit as YAML in Rancher UI and copy this values into the YAML:

      1.   longhornManager:
      2.     nodeSelector:
      3.       label-key1: "label-value1"
      4.   longhornDriver:
      5.     nodeSelector:
      6.       label-key1: "label-value1"
      7.   longhornUI:
      8.     nodeSelector:
      9.       label-key1: "label-value1"

    • If you install Longhorn by using kubectl to apply the deployment YAML, you need to modify the node selector section for Longhorn Manager, Longhorn UI, and Longhorn Driver Deployer. Then apply the YAMl files.

    • If you install Longhorn using Helm, you can change the Helm values for longhornManager.nodeSelector, longhornUI.nodeSelector, longhornDriver.nodeSelector in the values.yaml file. Then install the chart

  2. Set node selector for system managed components

    Follow the Customize default settings to set node selector by changing the value for the system-managed-components-node-selector default setting

    Note: Because of the limitation of Rancher 2.5.x, if you are using Rancher UI to install Longhorn, you need to click Edit As Yaml and add setting systemManagedComponentsNodeSelector to defaultSettings.

    For example:

    1. defaultSettings:
    2.   systemManagedComponentsNodeSelector: "label-key1:label-value1"

Setting up Node Selector After Longhorn has been installed

Warning:

  • Since all Longhorn components will be restarted, the Longhorn system is unavailable temporarily.
  • Make sure all Longhorn volumes are detached. If there are running Longhorn volumes in the system, this means the Longhorn system cannot restart its components and the request will be rejected.
  • Don’t operate the Longhorn system while node selector settings are updated and Longhorn components are being restarted.

  1. Prepare

    • If you are changing node selector in a way so that Longhorn cannot run on some nodes that Longhorn is currently running on, you will lose the volume replicas on those nodes. Therefore, It is recommended that you evict replicas and disable scheduling for those nodes before changing node selector. See Evicting Replicas on Disabled Disks or Nodes for more details about how to do this.
    • Stop all workloads and detach all Longhorn volumes. Make sure all Longhorn volumes are detached.

  2. Set node selector for user deployed components

    • If you install Longhorn by Rancher UI, you need to click Edit as YAML and copy this values into the YAML then click upgrade:

      1. longhornManager:
      2.   nodeSelector:
      3.     label-key1: "label-value1"
      4. longhornDriver:
      5.   nodeSelector:
      6.     label-key1: "label-value1"
      7. longhornUI:
      8.   nodeSelector:
      9.     label-key1: "label-value1"

    • If you install Longhorn by using kubectl to apply the deployment YAML, you need to modify the node selector section for Longhorn Manager, Longhorn UI, and Longhorn Driver Deployer. Then reapply the YAMl files.

    • If you install Longhorn using Helm, you can change the Helm values for longhornManager.nodeSelector, longhornUI.nodeSelector, longhornDriverDeployer.nodeSelector in the value.yaml file. Then do Helm upgrade the chart.

  3. Set node selector for system managed components

    The node selector setting can be found at Longhorn UI under Setting > General > System Managed Components Node Selector.

  4. Clean up

    If you are changing node selector in a way so that Longhorn cannot run on some nodes that Longhorn is currently running on, those nodes will become down state after this process. Verify that there is no replica left on those nodes. Disable scheduling for those nodes, and delete them in Longhorn UI

History

Available since v1.1.1