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Node Selectors

Node selectors are used to specify the nodes where a pod should be scheduled by using labels.

flowchart
  node1[Node 1]
  node2[Node 2]

Assume you have a pod that requires a GPU, but we know that Node 1 has GPU and Node 2 does not have a GPU. So, in this case, we want to schedule this pod on Node 1. There are two ways to achieve this:

  • Node Selectors
  • Node Affinity

Before we dive into Node Selectors, let's first understand how to label a node.

Bash
kubectl label nodes <node-name> <label-key>=<label-value>
kubectl label nodes node1 gpu=large

Then we only customize the pod definition file to include the node selector.

sample-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: sample-pod
spec:
  containers:
    - name: sample-container
      image: nginx
  nodeSelector:
    gpu: large

Now of course, this node selector method is not flexible enough to handle more complex scenarios. For example, if we want to schedule a pod on a node that has a large or medium GPU. We can't achieve this using node selectors. In this case, we need to use Node Affinity.