Resolving the cni plugin not initialized Error in Kubernetes 1.24+ with Flannel

Описание: A comprehensive guide on fixing the `cni plugin not initialized` error when using Kubernetes 1.24 and Flannel. Learn how to manage your network initialization challenges effectively!
---
This video is based on the question https://stackoverflow.com/q/73800970/ asked by the user 'Jim' ( https://stackoverflow.com/u/3712154/ ) and on the answer https://stackoverflow.com/a/73961924/ provided by the user 'Jim' ( https://stackoverflow.com/u/3712154/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Kubernetes 1.24+ fails with flannel giving "cni plugin not initialized"

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Introduction

If you've been working with Kubernetes, you may have encountered the error message cni plugin not initialized when using network plugins like Flannel after upgrading to version 1.24 or above. This issue can be frustrating, especially if everything functioned correctly in earlier versions. In this guide, we’ll dive into the root cause of this problem and provide you with detailed steps to resolve it.

The Problem

During a single-node Kubernetes installation on Ubuntu 20.04, users reported that the network would fail to initialize when using versions of Kubernetes greater than 1.23. The common symptoms include:

The node remains in a "NotReady" state.

The command describe nodes shows the KubeletNotReady error.

Flannel pods are running, but CoreDNS is stuck in a Pending state.

This situation often arises when the configuration or setup order is not properly aligned with the requirements of Kubernetes 1.24+.

Understanding the Solution

The key to resolving the cni plugin not initialized issue lies in the timing of how the network plugin is applied relative to the Kubernetes core DNS pods' initialization. Here's a simple breakdown of the solution steps.

Step 1: Initialization Command

Initially, when setting up your cluster, ensure you use the correct kubeadm init command. Here’s the command you should execute:

[[See Video to Reveal this Text or Code Snippet]]

This command configures your Kubernetes control-plane node properly but can encounter issues without subsequent adjustments.

Step 2: Wait for Pod States

Survey the Cluster Status: After running the initialization command, monitor the status of your CoreDNS pods using the following command:

[[See Video to Reveal this Text or Code Snippet]]

Check Pod Status: Look for pods in a Pending state. It is crucial that you allow these CoreDNS pods to indicate they are in a Pending state before moving forward.

Step 3: Apply the Network Plugin

After confirming that the CoreDNS pods have transitioned to a Pending state:

Apply Flannel: Proceed by applying the Flannel network plugin with the command:

[[See Video to Reveal this Text or Code Snippet]]

By waiting until the CoreDNS pods are in this state, you are helping ensure that the CNI plugins are initialized correctly, addressing the cni plugin not initialized error.

Why Does This Work?

Before Kubernetes version 1.24, the timing of these operations was less crucial. However, subsequent updates have introduced changes that require a more careful sequence of actions.

Conclusion

By following these steps and ensuring that you wait until the CoreDNS pods are in a Pending state before applying your network configuration, you can successfully resolve the initialization issues with the CNI plugins in Kubernetes 1.24 and later versions.

If you’re still experiencing problems after these adjustments, consider checking your environment settings related to network interfaces and ensuring that no conflicting services, like firewalls or network management software, are interfering with Docker or Kubernetes networking.

Experience smoother deployments and enrich your Kubernetes journey with this knowledge!