Kubernetes Taint Command

Introduction

In this lab, you will learn how to use the kubectl taint command, which is a powerful tool in Kubernetes for adding, modifying, and removing taints on nodes. Taints are used to indicate that a node has certain restrictions or requirements, and this can help control the scheduling of pods in a Kubernetes cluster.

Skills Graph

Start the Minikube Cluster

Before creating resources, you need a running Kubernetes cluster. Minikube is a lightweight Kubernetes environment that runs on your local machine.

1. Navigate to your working directory:

   Open the terminal and navigate to the default project folder:

   cd /home/labex/project

2. Start Minikube:

   Start Minikube to initialize a Kubernetes cluster:

   minikube start

   • This command sets up a single-node Kubernetes cluster on your local machine.
   • Minikube may take a few minutes to start depending on your system's performance.

3. Verify Minikube is running:

   Check the status of the Minikube cluster:

   minikube status

   • Look for components like kubelet and apiserver listed as Running.
   • If the cluster is not running, rerun minikube start.

If you encounter issues starting Minikube. Use minikube delete to reset the environment if needed.

Explore the kubectl taint Command

The kubectl taint command is used to add, modify, or remove taints on Kubernetes nodes. Taints are key-value pairs with effects that influence pod scheduling by restricting which pods can be placed on specific nodes.

Run the following command to view the available options for kubectl taint:

kubectl taint -h

You will see the following output:

Update the taints on one or more nodes.

  *  A taint consists of a key, value, and effect. As an argument here, it is expressed as key=value:effect.
  *  The key must begin with a letter or number, and may contain letters, numbers, hyphens, dots, and underscores, up to
  253 characters.
  *  Optionally, the key can begin with a DNS subdomain prefix and a single '/', like example.com/my-app.
  *  The value is optional. If given, it must begin with a letter or number, and may contain letters, numbers, hyphens,
  dots, and underscores, up to 63 characters.
  *  The effect must be NoSchedule, PreferNoSchedule or NoExecute.
  *  Currently taint can only apply to node.

Examples:
  ## Update node 'foo' with a taint with key 'dedicated' and value 'special-user' and effect 'NoSchedule'
  ## If a taint with that key and effect already exists, its value is replaced as specified
  kubectl taint nodes foo dedicated=special-user:NoSchedule

  ## Remove from node 'foo' the taint with key 'dedicated' and effect 'NoSchedule' if one exists
  kubectl taint nodes foo dedicated:NoSchedule-

  ## Remove from node 'foo' all the taints with key 'dedicated'
  kubectl taint nodes foo dedicated-

  ## Add a taint with key 'dedicated' on nodes having label mylabel=X
  kubectl taint node -l myLabel=X dedicated=foo:PreferNoSchedule

  ## Add to node 'foo' a taint with key 'bar' and no value
  kubectl taint nodes foo bar:NoSchedule

Add a Taint to a Node

In this step, you will learn how to add a taint to a node using the kubectl taint command. Taints are used to mark a node with certain restrictions or requirements, which can affect the scheduling of pods on that node.

To add a taint to a node, you can use the following command:

kubectl taint nodes minikube app=prod:NoSchedule

This will add a taint with key app and value prod to a node named minikube, with the effect NoSchedule. This will prevent pods from being scheduled on the node unless they tolerate the taint.

Then you can view the taints that are currently applied to nodes in your Kubernetes cluster using the kubectl describe node command.

To view the taints on a node, you can use the following command:

kubectl describe node minikube

The taints applied to the node will be listed under the "Taints" section in the output. You can use this information to verify that the taint you added in the previous step is applied to the node.

Remove a Taint From a Node

In this step, you will learn how to remove a taint from a node using the kubectl taint command. This can be useful if you need to update the restrictions or requirements of a node, or if you want to allow pods to be scheduled on a previously tainted node.

To remove a taint from a node, you can use the following command:

kubectl taint nodes minikube app-

It will remove the app=prod:NoSchedule taint from the minikube node. This will allow pods to be scheduled on the node without needing to tolerate the previously applied taint.

Modify a Taint on a Node

In this step, you will learn how to modify a taint on a node using the kubectl taint command. This can be useful if you need to update the restrictions or requirements of a node, but want to retain the existing taint key and effect.

1. Add a new taint with the following content:

kubectl taint nodes minikube app=uat:NoSchedule

2. Use overwrite to force updates

kubectl taint nodes minikube app=dev:NoSchedule --overwrite=true

It will update the app taint value from prod to dev on the minikube node. This will update the taint on the node while retaining the same taint key and effect.

Summary

In this lab, you learned how to use the kubectl taintcommand in Kubernetes. You started by adding a taint to a node using thekubectl taintcommand with a specific key, value, and effect. You then learned how to view the taints applied to a node using thekubectl describe node command.