Unlocking Efficiency: A Guide on Mastering the Kubectl Cordon Command

In the dynamic landscape of Kubernetes management, wielding the right commands can make all the difference. One such command, 'kubectl cordon,' stands out as a powerful tool for controlling node behavior within a cluster. In this guide, we will delve into the intricacies of the 'kubectl cordon' command, exploring its applications and providing a step-by-step walkthrough on how to leverage its capabilities.

Understanding the Kubectl Cordon Command:

Before we dive into the practical aspects, let's gain a solid understanding of what the 'kubectl cordon' command does. This command is designed to mark a node as unschedulable, meaning no new pods will be scheduled onto the node. However, existing pods on the node will continue to run.

Commands Overview:

To begin, let's familiarize ourselves with some basic commands related to 'kubectl cordon':

1. Check Node Status:

   kubectl get nodes
   

   This command displays a list of nodes in the cluster along with their current status.

2. Cordon a Node:

   kubectl cordon <node-name>
   

   Replace <node-name> with the actual name of the node you want to cordon.

3. Uncordon a Node:

   kubectl uncordon <node-name>
   

   This command reverses the effect of 'kubectl cordon' and allows new pods to be scheduled on the specified node.

Step-by-Step Instructions:

Step 1: Check Node Status

Before making any changes, it's essential to know the current state of the nodes in your Kubernetes cluster. Use the following command to display the node status:

kubectl get nodes

Identify the node you want to work with.

Step 2: Cordon the Node

To prevent new pods from being scheduled on the chosen node, use the 'kubectl cordon' command. Replace <node-name> with the actual name of your node:

kubectl cordon <node-name>

Verify the status change by re-running the 'kubectl get nodes' command.

Step 3: Uncordon the Node

If you wish to revert the node to a schedulable state, allowing new pods, use the 'kubectl uncordon' command:

kubectl uncordon <node-name>

More Examples:

Example 1: Cordon and Uncordon in One Command

You can combine both actions into a single command:

kubectl cordon <node-name> && sleep 5 && kubectl uncordon <node-name>

This command cordon the node, waits for 5 seconds, and then uncordons it.

Example 2: Use Label Selectors

Cordon nodes based on label selectors:

kubectl cordon -l <label-key>=<label-value>

This command cordon nodes that match the specified label key and value.