A node selector specifies a map of key-value pairs. The rules are defined using custom labels on nodes and selectors specified in pods.

For the pod to be eligible to run on a node, the pod must have the indicated key-value pairs as the label on the node.

If you are using node affinity and node selectors in the same pod configuration, see the important considerations below.

Using node selectors to control pod placement

You can use node selector labels on pods to control where the pod is scheduled.

You then add labels to a specific nodes where you want the pods scheduled or to the MachineSet that controls the nodes.

You can add labels to a node or MachineConfig, but the labels will not persist if the node or machine goes down. Adding the label to the MachineSet ensures that new nodes or machines will have the label.

  1. Add the desired node selector on your pod.

    For example, make sure that your pod configuration features the nodeSelector value indicating the desired label:

    apiVersion: v1
    kind: Pod
        <key>: <value>

    For example:

    apiVersion: v1
    kind: Pod
        region: east
        type: user-node
  2. Add the label to your nodes:

    $ oc label <resource> <name> <key>=<value>

    For example, to label a node:

    $ oc label nodes ip-10-0-142-25.ec2.internal type=user-node region=east

    To label a MachineSet:

    $ oc label MachineSet abc612-msrtw-worker-us-east-1c type=user-node region=east

    The label is applied to the node:

    kind: Node
    apiVersion: v1
      name: ip-10-0-131-14.ec2.internal
      selfLink: /api/v1/nodes/ip-10-0-131-14.ec2.internal
      uid: 7bc2580a-8b8e-11e9-8e01-021ab4174c74
      resourceVersion: '478704'
      creationTimestamp: '2019-06-10T14:46:08Z'
        beta.kubernetes.io/os: linux
        failure-domain.beta.kubernetes.io/zone: us-east-1a
        node.openshift.io/os_version: '4.1'
        node-role.kubernetes.io/worker: ''
        failure-domain.beta.kubernetes.io/region: us-east-1
        node.openshift.io/os_id: rhcos
        beta.kubernetes.io/instance-type: m4.large
        kubernetes.io/hostname: ip-10-0-131-14
        region: east (1)
        beta.kubernetes.io/arch: amd64
        type: user-node (1)
    1 Label added to the node.

If you are using node selectors and node affinity in the same pod configuration, note the following:

  • If you configure both nodeSelector and nodeAffinity, both conditions must be satisfied for the pod to be scheduled onto a candidate node.

  • If you specify multiple nodeSelectorTerms associated with nodeAffinity types, then the pod can be scheduled onto a node if one of the nodeSelectorTerms is satisfied.

  • If you specify multiple matchExpressions associated with nodeSelectorTerms, then the pod can be scheduled onto a node only if all matchExpressions are satisfied.