Scheduling Pods with taints and tolerations #

A taint and toleration can be defined in KWOK. It’s handy in these situations:

You have KWOK installed in your real cluster (KIND, K3D, etc.), and you want some or all of your pods to be scheduled to the KWOK nodes to test for scalability.
You want to simulate taint and toleration use cases within a KWOK cluster.

Let’s look at point 2 for now.

This image shows you what you should expect when testing this scenario. You can follow the step-by-step guide after seeing this.

Prerequisites #

KWOK must be installed on the machine. See installation.
Install kubectl

Create cluster #

kwokctl create cluster

View clusters #

This ensures that the cluster was created successfully.

kwokctl get clusters

Create a node #

kwokctl scale node --replicas 1

Taint node #

kubectl taint nodes node-000000 kwok.x-k8s.io/node=fake:NoSchedule

Deploy a pod without toleration and observe #

no-toleration-pod.yaml ↕

apiVersion: v1
kind: Pod
metadata:
  name: no-toleration-pod
  namespace: default
spec:
  containers:
  - name: fake-container
    image: fake-image
    ports:
    - containerPort: 80

kubectl apply -f no-toleration-pod.yaml
kubectl get pod

NAME                READY   STATUS    RESTARTS   AGE
no-toleration-pod   0/1     Pending   0          4s

The pod is stuck in a pending state.

Deploy a pod with toleration and observe #

with-toleration-pod.yaml ↕

apiVersion: v1
kind: Pod
metadata:
  name: with-toleration-pod
  namespace: default
spec:
  containers:
  - name: fake-container
    image: fake-image
    ports:
    - containerPort: 80
  tolerations:
  - key: "kwok.x-k8s.io/node"
    operator: "Exists"
    effect: "NoSchedule"

kubectl apply -f with-toleration-pod.yaml

kubectl get pod

NAME                    READY   STATUS    RESTARTS   AGE
no-toleration-pod       0/1     Pending   0          20s
with-toleration-pod     1/1     Running   0          2s

Only the pod with toleration is in a running state.

Delete the cluster #

kwokctl delete cluster

Conclusion #

This example demonstrates how to use KWOK to simulate a scheduling scenario based on taints and tolerations policy.