Troubleshooting Multus CNI Error Failed To Get Cached Delegates File In Kubernetes

by StackCamp Team 83 views

Hey everyone! Today, we're diving deep into a common issue you might encounter when using Multus CNI in your Kubernetes clusters: the dreaded failed to get the cached delegates file error. If you're seeing this in your logs, don't worry, you're not alone! This article will walk you through the problem, why it happens, and how to fix it. Let's get started!

Understanding the Multus CNI Error

So, what exactly does this error message mean? The Multus: failed to get the cached delegates file: open /var/lib/cni/multus/... no such file or directory, cannot properly delete error typically pops up when Multus CNI is trying to clean up after a Pod has been terminated. Multus, as you may know, is a powerful CNI plugin that allows you to attach multiple network interfaces to your Pods. It achieves this by using delegate network configurations, which are essentially instructions on how to set up these additional networks. When a Pod is deleted, Multus needs to clean up these configurations, and that's where this error can occur.

Why This Error Happens

There are a few key reasons why you might be seeing this error:

  1. Timing Issues: The most common cause is a timing issue during the Pod deletion process. Multus might be trying to access the cached delegate file after it has already been removed by the system. This can happen if the cleanup process is not perfectly synchronized with the Pod's lifecycle.
  2. File System Inconsistencies: In some cases, there might be inconsistencies in the file system where Multus stores its cached files. This could be due to underlying storage issues or problems with the container runtime.
  3. Configuration Problems: Although less common, misconfigurations in your Multus setup can also lead to this error. For example, if Multus is not properly configured to access the necessary files and directories, it might fail to retrieve the cached delegate file.

To put it simply, this error arises when Multus attempts to access a cached configuration file for a network delegate, but that file is either missing or inaccessible. This usually occurs during the pod deletion process, where Multus attempts to clean up the network configurations associated with the pod. The file it's looking for is typically located in /var/lib/cni/multus/, and the filename is a unique identifier associated with the pod and its network configuration. When Multus can't find this file, it logs the failed to get the cached delegates file error. Understanding these reasons is the first step in effectively troubleshooting and resolving the issue. In the next sections, we'll dive into specific scenarios and solutions to help you tackle this problem head-on.

Analyzing the Error Logs and Environment

Okay, so you've seen the error message. Now, let's break down how to analyze the logs and your environment to pinpoint the exact cause. Remember, the more information you gather, the easier it will be to find a solution. So, let’s get into the details so you can figure out what’s happening in your setup.

Examining the Logs

First up, let’s dive into those logs. The error message you provided gives us some crucial clues:

2025-09-30T12:38:33Z [debug] GetK8sClient: /etc/cni/net.d/multus.d/multus.kubeconfig, <nil>
2025-09-30T12:38:33Z [debug] GetPod for [multus/samplepod-no-multus-896fdb9db-2gq4s] starting
2025-09-30T12:38:33Z [debug] isCriticalRequestRetriable: pods "samplepod-no-multus-896fdb9db-2gq4s" not found
2025-09-30T12:38:33Z [debug] GetPod for [multus/samplepod-no-multus-896fdb9db-2gq4s] took 7.868473ms
2025-09-30T12:38:33Z [error] Multus: GetPod failed: pod not found during Multus GetPod, but continue to delete
2025-09-30T12:38:33Z [debug] consumeScratchNetConf: b54a511ce85259553e468996bc90ce0f9abd18bedc25806b6b7c7211c68ea6a7, /var/lib/cni/multus
2025-09-30T12:38:33Z [error] Multus: failed to get the cached delegates file: open /var/lib/cni/multus/b54a511ce85259553e468996bc90ce0f9abd18bedc25806b6b7c7211c68ea6a7: no such file or directory, cannot properly delete

Let's break it down:

  • GetPod failed: pod not found: This is a key piece of information. It indicates that Multus is trying to get information about a Pod (samplepod-no-multus-896fdb9db-2gq4s) that no longer exists. This strongly suggests a timing issue during Pod deletion.
  • failed to get the cached delegates file: This is the error we're focusing on. It confirms that Multus can't find the cached delegate file associated with the Pod.
  • open /var/lib/cni/multus/...: no such file or directory: This tells us the exact location where Multus is looking for the file and confirms that it's missing.

So, the logs are pointing towards a race condition where Multus is trying to clean up a Pod's network configuration after the Pod has already been removed.

Examining the Environment

Next, let's look at your environment configuration. The provided information gives us some important details:

  • Multus version: 4.2.2
  • Kubernetes version: v1.31.5
  • Primary CNI: Calico
  • OS: Garden Linux 1931.0
  • Multus deployment: Deployed via DaemonSet in thin mode.

Key things to note:

  • Thin Mode: Multus is running in thin mode, which means it doesn't cache all the delegate configurations in memory. Instead, it reads them from disk each time. This can make it more susceptible to timing issues if the files are deleted before Multus can access them.
  • CNI Configuration: The 00-multus.conf file shows that Multus is configured to use Calico as the primary CNI and includes settings for logging, kubeconfig, and delegates. This configuration looks generally correct, but it's always good to double-check for any typos or misconfigurations.

By combining the information from the logs and the environment, we can start to form a clearer picture of what's going on. The timing issue seems to be the most likely culprit here, especially given the thin mode deployment. In the next section, we'll explore potential solutions to address this problem.

Potential Solutions and Workarounds

Alright, guys, now that we've dissected the error and analyzed the environment, let's move on to the good stuff: how to fix it! While this error can be a bit annoying, there are several potential solutions and workarounds we can try.

1. Adjusting Multus Configuration

One approach is to tweak the Multus configuration to be more resilient to timing issues. Here are a couple of things you can try:

  • Increase the Retry Interval: Multus has some built-in retry mechanisms. You can try increasing the interval between retries to give it more time to find the cached files. This can be done by adding or modifying parameters in the Multus DaemonSet configuration.
  • Disable Caching (Use with Caution): Although not generally recommended, you could try disabling caching altogether. This would force Multus to always read the delegate configurations from disk, which might avoid the error if the files are consistently present. However, this can impact performance, so use this option as a last resort.

2. Kubernetes Pod Lifecycle Management

Another strategy is to look at how Kubernetes is managing Pod lifecycles. Sometimes, the timing issues are exacerbated by aggressive Pod deletion policies. Consider these adjustments:

  • Graceful Termination: Ensure that your Pods are configured to terminate gracefully. This means allowing them to finish their current tasks and clean up resources before being forcibly terminated. You can configure this using the terminationGracePeriodSeconds setting in your Pod specifications.
  • Pod Disruption Budgets (PDBs): If you're using PDBs, make sure they are configured correctly to avoid disruptions during updates or deployments. PDBs can help prevent Pods from being deleted prematurely, which can reduce the chances of timing issues.

3. Addressing Underlying Storage Issues

In some cases, the error might be caused by problems with the underlying storage system. If you suspect this, investigate the following:

  • File System Health: Check the health of the file system where Multus stores its cached files (usually /var/lib/cni/multus). Look for any errors or warnings in the system logs.
  • Storage Performance: If the storage is slow or experiencing latency, it can contribute to timing issues. Monitor the performance of your storage system and consider optimizing it if necessary.

4. Workaround: Ignoring the Error (Temporarily)

Okay, so this isn't a solution per se, but it's a pragmatic workaround in some situations. The error failed to get the cached delegates file is often logged even when the cleanup is otherwise successful. So, if you're seeing this error but everything else seems to be working fine, you might choose to simply ignore it for the time being. This isn't ideal, but it can buy you some time while you investigate the underlying issue more thoroughly. However, make sure to monitor your system closely to ensure there are no other problems.

5. Upgrading Multus and Kubernetes

Finally, consider upgrading Multus and Kubernetes to the latest stable versions. Newer versions often include bug fixes and performance improvements that can address these kinds of issues. Check the release notes for any relevant fixes related to CNI and Pod lifecycle management.

By trying out these solutions, you'll be well on your way to resolving the failed to get the cached delegates file error. Remember to test each solution in a non-production environment first to ensure it doesn't introduce any unexpected issues. In the next section, we'll wrap up with a summary and some best practices.

Best Practices and Summary

Alright, we've covered a lot of ground, guys! Let's wrap things up with a quick summary and some best practices to keep in mind when working with Multus and Kubernetes networking.

Summary of Solutions

To recap, here are the main solutions we discussed for the failed to get the cached delegates file error:

  1. Adjusting Multus Configuration: Tweak retry intervals or, as a last resort, disable caching.
  2. Kubernetes Pod Lifecycle Management: Ensure graceful termination and proper PDB configuration.
  3. Addressing Underlying Storage Issues: Check file system health and storage performance.
  4. Workaround: Ignoring the Error (Temporarily): If cleanup is successful otherwise, monitor and investigate later.
  5. Upgrading Multus and Kubernetes: Use the latest stable versions for bug fixes and improvements.

Best Practices for Multus and Kubernetes Networking

To prevent issues like this from cropping up in the first place, here are some best practices to follow:

  • Monitor Your Logs: Regularly check your Multus and Kubernetes logs for errors and warnings. This proactive approach can help you catch issues early before they escalate.
  • Keep Multus and Kubernetes Updated: As mentioned earlier, staying up-to-date with the latest versions is crucial for bug fixes and performance enhancements.
  • Understand Your Network Configuration: Make sure you have a solid understanding of your network configuration, including your primary CNI (Calico in this case) and any additional network attachments.
  • Test Your Configurations: Always test your Multus configurations in a non-production environment before deploying them to production. This helps you identify potential issues and avoid disruptions.
  • Use Graceful Termination: Configure your Pods to terminate gracefully to minimize timing issues during deletion.
  • Properly Configure Pod Disruption Budgets: If you're using PDBs, make sure they are set up correctly to avoid premature Pod deletions.

Final Thoughts

The failed to get the cached delegates file error in Multus CNI can be a bit of a head-scratcher, but with a systematic approach, you can definitely resolve it. Remember to analyze your logs, examine your environment, and try the solutions we've discussed. And most importantly, follow best practices to keep your Kubernetes networking running smoothly.

By understanding the root causes and implementing these solutions, you'll be well-equipped to handle this error and ensure your Multus-powered Kubernetes clusters are running smoothly. Keep experimenting, keep learning, and happy networking!