Certified Kubernetes Administrator Study Guide – Scheduling – Use label selectors to schedule pods

• Labels are key-value pairs
• When using label selectors to specify node selection you add the following section to the yaml specification:

nodeSelector:
  accelerator: nvidia-tesla-p100

This example is telling Kubernetes to select only nodes with the label accelerator = nvidia-tesla-p100.

Where accelerator is the is the key and nvidia-tesla-p100 is the value.

• The nodeSelector section comes within the spec: section after the definition of the containers.
• Matching resources must satisfy all of the specified label constraints, although they can have additional labels as well e.g. the above example requires that a node has a label of accelerator with a value of nvidia-tesla-p100 in order to match the selector for the pod but it could also have a label of production with a value of true. The pod does not have to have this label specified in its selector statement.
• Can also create a label on a node using kubectl:

kubectl label node vm-node1 environment=production

• For services and replicationcontrollers targeting a set of pods label selectors are also used in this scenario they use the format:

selector:{
  "component": "redis",
}

  or

selector:
  component: redis

Can use kubectl with labels using:

kubectl get pods -l environment=production, tier=frontend