Demystifying Taints and Tolerations in Kubernetes: Everything you Need to Know

Introduction

Kubernetes is a powerful container orchestration system that helps automate the deployment, scaling, and management of containerized applications. One of the features that make Kubernetes powerful is its ability to schedule pod placements based on available resources, which it does by default without any manual intervention.

But what if you have a specific set of nodes you want to use to deploy your apps or certain pods, which require specific nodes or configurations?

This is where Kubernetes taints and tolerations come in.

Taints and tolerations are Kubernetes’ way of indicating the nodes that allow or disallow the scheduling of pods into them. In this blog post, we’ll dive into the basics of taints and tolerations and cover how you can implement them in your Kubernetes environment to tight control where specific workloads are running.

Taints

A taint is a property or attribute that marks a node to prevent new pods from being scheduled to it unless the pod has a corresponding toleration. They are used to mark nodes as unsuitable or restricted for scheduling certain types of workloads, signaling that they should only be used for specific use cases or to prevent accidental deployment.

In Kubernetes, there are three types of taints that can be applied to nodes:

• NoSchedule: prevents any new pods from being scheduled to that node except those that specify a toleration for that taint.

• PreferNoSchedule: indicates that Kubernetes will try not to schedule pods to that node unless there's no other alternative available.

• NoExecute: forces any new and existing pods running on that node to terminate.

To add a taint to a node, you can use the kubectl taint command, providing the node name, taint key, and value, as well as the effect type. Here's an example for adding a NoSchedule taint to a node:

kubectl taint nodes node1 key=value:NoSchedule

This command adds a NoSchedule taint with the key key and value value to the node named node1.

Tolerations

Tolerations, on the other hand, are used to evade taints that mark nodes and allow pods to be scheduled on them. A toleration is an attribute added to pod specifications that signifies it can be scheduled to a node with a matching taint.

To add a toleration to a pod's specification, create a tolerations field with the taint key, value, and effect that the pod can tolerate.

Here's an example of a Pod specification containing a toleration for the taint key and value mentioned in the earlier example:

apiVersion: v1
kind: Pod
metadata:
  labels:
    app: example
  name: example-pod
spec:
  containers:
  - image: nginx
    name: nginx
  tolerations:
  - key: "key"
    operator: "Equal"
    value: "value"
    effect: "NoSchedule"

This specification adds a toleration to the Pod that matches the key, value and effect of the NoSchedule taint added to the node.

Conclusion

Kubernetes taints and tolerations are powerful mechanisms that allow administrators to control where workloads are placed within a cluster. They help to ensure that pods are scheduled only on appropriate nodes and maintain a healthy working environment by preventing accidental deployment.

In conclusion, taints and tolerations provide a way to enforce node selection policies for pods based on specific node requirements or configurations. When used together, they help create a robust environment for deploying workloads in a way that ensures the correct nodes are used for specific applications.

By using the appropriate taints and tolerations, you can control which nodes are eligible to schedule certain pods, ensuring a stable environment for both development and production environments.