Exercise

  1. Add the label disktype=ssd on the worker1 Node

  2. Create the specification of a Pod named nginx based on the nginx:1.26 image.

  3. Modify the specification making sure the Pod is scheduled on the Node worker1 and requests 1.5Gi of memory. Then create the resource and verify the Pod is running.

Note: if your Pod stays in Pending you can use a lower value for the memory request to make sure it get deployed.

  1. Get the Pod’s priority and priorityClassName

  2. Create a new PriorityClass named high with value 100000

  3. Create a new Pod named apache based on the httpd:2.4 image, making sure it is scheduled on the Node worker1, it has the same memory request as the Pod nginx and it uses the priorityClass high. Once created, get the Pod’s priority.

  4. What happened ?

  5. Delete the Pods, the PriorityClass, and remove the disktype label from worker1

Documentation

https://kubernetes.io/docs/concepts/scheduling-eviction/pod-priority-preemption/#priorityclass


Solution
  1. Add the label disktype=ssd on the worker1 Node
kubectl label node worker1 disktype=ssd
  1. Create the specification of a Pod named nginx based on the nginx:1.26 image.
kubectl run nginx --image=nginx:1.26 --dry-run=client -o yaml > pod.yaml
  1. Modify the specification making sure the Pod is scheduled on the Node worker1 and requests 1.5Gi of memory. Then create the resource and verify the Pod is running.

Modification of the specification to add the specific constraints:

pod.yaml
apiVersion: v1
kind: Pod
metadata:
  labels:
    run: nginx
  name: nginx
spec:
  nodeSelector:
    disktype: ssd
  containers:
  - image: nginx:1.26
    name: nginx
    resources:
      requests:
        memory: 1.5Gi

Creation of the resource:

kubectl apply -f pod.yaml

Make sure the Pod is running:

kubectl get po/nginx
  1. Get the Pod’s priority and priorityClassName

Pod’s priority is 0:

kubectl get po/nginx -o jsonpath={.spec.priority}
0

Pod’s priorityClassName is not defined

kubectl get po/nginx -o jsonpath={.spec.priorityClassName}
  1. Create a new PriorityClass named high with value 100000
cat <<EOF | kubectl apply -f -
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: high
value: 1000000
globalDefault: false
EOF
  1. Create a new Pod named apache based on the httpd:2.4 image, making sure it is scheduled on the Node worker1, it has the same memory request as the Pod nginx and it uses the priorityClass high. Once created, get the Pod’s priority.
cat<<EOF | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  labels:
    run: apache
  name: apache
spec:
  priorityClassName: high
  nodeSelector:
    disktype: ssd
  containers:
  - image: httpd:2.4
    name: apache
    resources:
      requests:
        memory: 1.5Gi
EOF

Get the Pod’s priority:

kubectl get po/apache -o jsonpath={.spec.priority}
1000000
  1. What happened ?

Listing the Pods we can see the nginx one is not present anymore:

kubectl get po
NAME     READY   STATUS    RESTARTS   AGE
apache   1/1     Running   0          14s

As the apache Pod has a higher priority than the nginx once, and because the Node worker1 does not have enough resources to run both of them, the nginx Pod has been evicted and replaced by the apache one.

We can see the preemption in the events as well:

kubectl get events
...
27s         Normal    Preempted          pod/nginx                 Preempted by default/apache on node worker1
  1. Delete the Pods, the PriorityClass, and remove the disktype label from worker1

The nginx Pod has already been removed

kubectl delete po/apache priorityClass/high
kubectl label node worker1 disktype-