Helm Install Pod Crash On Superseded State Issue And Reproduction

Hey guys! Today, we're diving deep into a tricky issue in the Kubernetes world, specifically focusing on how Helm install pods behave when they encounter a superseded state. This is a common problem, especially when dealing with Helm deployments in environments like K3s and RKE2. We'll break down the problem, show you how to reproduce it, and discuss why it's happening. So, buckle up and let's get started!

Understanding the Superseded State in Helm

Before we jump into the nitty-gritty details, let's quickly define what a superseded state means in Helm. In Helm, each deployment is tracked as a release. Whenever you make a change to your deployment (like updating a value or rolling back), Helm creates a new revision of that release. These revisions are stored as secrets in Kubernetes. Now, if a release revision is deleted – maybe accidentally or due to some cleanup process – the Helm release can enter a superseded state. This means that Helm knows the release exists, but it can't find the latest revision data. Understanding this superseded state is crucial for troubleshooting issues related to Helm deployments, especially when encountering errors during updates or rollbacks. When a Helm release enters a superseded state, it essentially means that the historical record of the release is incomplete or inconsistent, leading to potential conflicts and failures in subsequent operations. Imagine it like a book with missing pages – the story is there, but you can't quite follow the latest chapter. This can happen due to various reasons, such as accidental deletion of secrets, manual intervention, or issues with the underlying storage system. Therefore, recognizing and addressing the superseded state is a critical aspect of maintaining a healthy and stable Kubernetes environment when using Helm for package management. By understanding the implications of this state, you can proactively prevent issues and implement strategies for recovery and remediation. For instance, regular backups of your Kubernetes secrets can safeguard against accidental data loss, ensuring that you can restore your Helm releases to a consistent state. Additionally, monitoring your Helm releases for superseded states can help you identify and address potential problems before they escalate into more serious disruptions. In essence, a superseded state in Helm serves as a warning sign that something has gone amiss with your release history, prompting you to investigate and take corrective action to restore the integrity of your deployments. So, keeping a close eye on the status of your Helm releases and understanding the implications of the superseded state are essential practices for anyone managing applications in Kubernetes with Helm. This proactive approach will not only help you troubleshoot issues more effectively but also ensure the long-term stability and reliability of your deployments. Remember, Helm is a powerful tool for managing Kubernetes applications, but like any tool, it requires a solid understanding of its inner workings to use it effectively.

The Problem: Helm Install Pod Crash Loop

Okay, so here’s the core issue. When a Helm release is in a superseded state, the helm-install pod (which is responsible for deploying and updating Helm charts in K3s and other Kubernetes distributions) doesn't handle this gracefully. Instead of recognizing the superseded state and attempting an upgrade or a reconciliation, it falls back to the helm install command. This is where the trouble starts. The helm install command is designed to create new releases, not to update existing ones. So, when it tries to install a release with the same name as the superseded one, it throws an error: Error: INSTALLATION FAILED: cannot re-use a name that is still in use. This error causes the helm-install pod to crash, and because it's in a deployment, Kubernetes tries to restart it, leading to a crash loop. This crash loop scenario highlights a critical gap in the helm-install pod's logic. It's not equipped to handle the complexities of a superseded release, which requires a different approach than a fresh installation. The pod's inability to differentiate between a new deployment and an update to a superseded release results in a repeated cycle of failure. Each time the pod restarts, it attempts the same installation process, encountering the same error and crashing again. This continuous crash loop not only disrupts the deployment process but also consumes valuable resources, potentially impacting the overall performance of the Kubernetes cluster. The underlying problem is that the helm install command, by design, is intended for initial deployments and is not capable of reconciling a release that is in a superseded state. When a release is superseded, it signifies that there is a discrepancy between the current state of the release and its historical record. Resolving this discrepancy typically requires a Helm upgrade or a rollback operation, which are specifically designed to handle updates and revisions of existing releases. The helm-install pod's failure to recognize and handle this scenario underscores the importance of implementing robust error handling and state management in Kubernetes controllers. A well-designed controller should be able to identify different states of a resource, such as a Helm release, and take appropriate actions based on the current state. In the case of a superseded release, the controller should ideally attempt a Helm upgrade or a rollback to restore the release to a consistent state, rather than attempting a fresh installation. Furthermore, the crash loop situation emphasizes the need for effective monitoring and alerting in Kubernetes environments. When a pod enters a crash loop, it's a clear indication of a problem that requires immediate attention. Setting up alerts for pod failures can help you quickly identify and address issues before they escalate into more significant disruptions. By proactively monitoring your deployments and responding to errors in a timely manner, you can minimize the impact of issues like the helm-install pod crash loop and maintain the stability of your Kubernetes cluster.

Reproducing the Issue: Step-by-Step Guide

Let's walk through a step-by-step guide on how to reproduce this issue. This will help you understand the problem firsthand and potentially test any fixes or workarounds. Follow these steps carefully:

Step 1: Set up a Kubernetes Cluster

First, you'll need a Kubernetes cluster. For this demonstration, we'll use RKE2, but K3s or any other Kubernetes distribution should work similarly. Make sure you have ingress-nginx installed in your cluster. This is a common component, and we'll be using it as our example deployment. Having a properly configured Kubernetes cluster is the foundational step for reproducing this issue. Without a running cluster, you won't be able to deploy Helm charts or observe the behavior of the helm-install pod. Therefore, ensuring that your cluster is up and running, and that you have the necessary tools like kubectl configured to interact with it, is crucial before proceeding with the subsequent steps. RKE2 and K3s are both lightweight Kubernetes distributions that are well-suited for testing and development purposes. They provide a streamlined installation process and a minimal footprint, making them ideal for experimenting with Kubernetes features and troubleshooting issues. If you're using a different Kubernetes distribution, such as Minikube or a cloud-based service like Google Kubernetes Engine (GKE) or Amazon Elastic Kubernetes Service (EKS), the steps might vary slightly, but the core concepts remain the same. Regardless of the distribution you choose, make sure that you have the necessary permissions and access to deploy resources and manage your cluster. Once your cluster is up and running, you'll need to install ingress-nginx. Ingress-nginx is an Ingress controller for Kubernetes that uses Nginx as a reverse proxy and load balancer. It allows you to expose your services to the outside world by defining Ingress resources that route traffic to your applications. Ingress-nginx is a common component in Kubernetes deployments, and it's a good example to use for reproducing this issue because it's a relatively complex application that involves multiple Kubernetes resources, such as Deployments, Services, and ConfigMaps. If you already have ingress-nginx installed in your cluster, you can skip this step. However, if you don't have it installed, you'll need to follow the installation instructions for your specific Kubernetes distribution. Typically, this involves deploying a Helm chart or applying a set of YAML manifests to your cluster. Once you have your Kubernetes cluster and ingress-nginx set up, you're ready to move on to the next step, which involves creating a HelmChartConfig to manage the ingress-nginx deployment. This configuration will serve as the basis for our experiment, allowing us to observe how the helm-install pod behaves when we introduce a superseded state into the Helm release.

Step 2: Create a HelmChartConfig

Now, create a HelmChartConfig resource. This is a custom resource definition (CRD) provided by Rancher's Helm controller, which is used in K3s and RKE2 to manage Helm charts. Here’s an example HelmChartConfig you can use:

apiVersion: helm.cattle.io/v1
kind: HelmChartConfig
metadata:
  name: rke2-ingress-nginx
  namespace: kube-system
spec:
  valuesContent: |-
    controller:
      metrics:
        enabled: true
        serviceMonitor:
          enabled: true
          additionalLabels:
            foo: "bar"

This HelmChartConfig tells the Helm controller to deploy the ingress-nginx chart with some custom values, specifically enabling metrics and adding a label. The HelmChartConfig is a crucial component in this setup because it allows us to manage the deployment of Helm charts in a declarative manner. By defining the desired state of the chart in the HelmChartConfig, we can ensure that the Helm controller will automatically deploy and maintain the chart according to our specifications. This approach is particularly beneficial in Kubernetes environments, where declarative configuration management is a key principle. The HelmChartConfig resource includes several important fields, such as the chart name, the namespace where the chart should be deployed, and the valuesContent field, which allows us to customize the chart's configuration. In this example, we're using the valuesContent field to enable metrics and add a custom label to the ingress-nginx deployment. These customizations are not essential for reproducing the issue, but they help to illustrate how the HelmChartConfig can be used to configure Helm charts according to your specific requirements. When you create a HelmChartConfig resource in your Kubernetes cluster, the Helm controller will automatically detect the change and initiate the deployment process. The controller will fetch the specified chart from the configured Helm repository, apply the customizations defined in the valuesContent field, and deploy the chart to the target namespace. The controller also monitors the deployed chart and ensures that it remains in the desired state. If any changes are made to the HelmChartConfig, the controller will automatically update the deployment to reflect the changes. This automated management of Helm charts simplifies the deployment and maintenance of applications in Kubernetes, reducing the risk of human error and ensuring that your deployments are always in a consistent state. So, by creating a HelmChartConfig for ingress-nginx, we're setting the stage for reproducing the issue by establishing a baseline deployment that we can then manipulate to create a superseded state. This controlled environment allows us to observe the behavior of the helm-install pod and understand the root cause of the problem.

Step 3: Wait for the Deployment

Give the Helm controller some time to deploy the chart. You can check the progress by watching the helm-install pods in the kube-system namespace:

kubectl get po -n kube-system | grep helm-install

Once the pod is in a Running state, the deployment should be complete. Waiting for the deployment to complete is a critical step in this process. The helm-install pod needs to successfully deploy the ingress-nginx chart before we can proceed with the next steps, which involve manipulating the release history to create a superseded state. Rushing through this step could lead to inaccurate results or make it difficult to reproduce the issue reliably. The helm-install pod is responsible for executing the Helm commands necessary to deploy and manage the chart. It typically runs as a Job in Kubernetes, which means that it will start a pod, perform its task, and then terminate. The pod logs provide valuable information about the deployment process, including any errors or warnings that might have occurred. By monitoring the helm-install pods, you can gain insights into the progress of the deployment and identify any potential problems. If the pod is stuck in a Pending state, it could indicate that there are insufficient resources in your cluster to schedule the pod. If the pod is in a CrashLoopBackOff state, it means that the pod has crashed repeatedly, and Kubernetes is attempting to restart it. In this case, you should examine the pod logs to understand the cause of the crashes. Once the helm-install pod is in a Running state, it indicates that the deployment has likely been successful. However, it's still a good idea to verify the deployment by checking the status of the deployed resources, such as Deployments, Services, and Ingresses. You can use kubectl commands to check the status of these resources and ensure that they are in the desired state. For example, you can use kubectl get deployments -n kube-system to check the status of the ingress-nginx Deployment. If the deployment is successful, you should see that the desired number of replicas are running and that the deployment is available. Similarly, you can use kubectl get services -n kube-system to check the status of the ingress-nginx Service and ensure that it's properly configured. By verifying the deployment, you can confirm that the Helm chart has been deployed correctly and that the application is running as expected. This ensures that you have a clean starting point for the next steps, which involve manipulating the Helm release history to create a superseded state. So, taking the time to wait for the deployment to complete and verify its status is an essential part of the process, ensuring that you can accurately reproduce the issue and understand its root cause.

Step 4: Check the Helm Status

Verify that the Helm release is in the deployed state:

helm ls -n kube-system | grep ingress

You should see output similar to this, with the STATUS column showing deployed:

NAME                    NAMESPACE       REVISION        UPDATED                                 STATUS          CHART                           APP VERSION
rke2-ingress-nginx      kube-system     2               2023-10-27 14:30:00.123456789 +0000 UTC deployed        ingress-nginx-4.5.2             1.9.0

Checking the Helm status is a crucial step in confirming that the initial deployment was successful and that we have a baseline from which to work. The helm ls command provides a summary of the Helm releases in a specified namespace, including the release name, namespace, revision number, update timestamp, status, chart name, and application version. By filtering the output using grep ingress, we can focus specifically on the ingress-nginx release that we deployed in the previous steps. The STATUS column in the output is particularly important, as it indicates the current state of the release. A status of deployed confirms that the release was successfully installed and is currently running in the cluster. If the status is anything other than deployed, such as pending-install, failed, or superseded, it indicates that there is a problem with the release, and you should investigate further before proceeding. A pending-install status suggests that the release is still in the process of being deployed. This could be due to various reasons, such as a slow network connection, insufficient resources in the cluster, or errors in the chart itself. If the release remains in this state for an extended period, you should check the logs of the helm-install pod for any error messages. A failed status indicates that the release failed to install or upgrade. This could be due to various reasons, such as invalid chart syntax, missing dependencies, or conflicts with existing resources. The Helm CLI typically provides error messages that can help you diagnose the cause of the failure. A superseded status, as we discussed earlier, indicates that a newer revision of the release has been deployed, and the current revision is no longer the active one. This status is expected in scenarios where you have upgraded the release or rolled back to a previous version. However, in our case, we are intentionally going to create a superseded state by deleting a release secret, which is an abnormal situation. If you see a superseded status at this stage, it could indicate that something went wrong during the initial deployment, and you should investigate before proceeding. By verifying the Helm status, we ensure that the ingress-nginx release is in a healthy state before we start manipulating the release history. This helps us to isolate the issue and confirm that the helm-install pod's behavior is specifically related to the superseded state that we are going to create. So, taking the time to check the Helm status is an essential step in the process, ensuring that we have a solid foundation for reproducing the issue and understanding its root cause.

Step 5: Check the Release Secrets

Helm stores release information as secrets in Kubernetes. List the secrets in the kube-system namespace and look for those related to the ingress release:

kubectl get secrets -n kube-system | grep ingress | grep helm.release

You'll see secrets like this:

sh.helm.release.v1.rke2-ingress-nginx.v1                     helm.sh/release.v1                 1      119d
sh.helm.release.v1.rke2-ingress-nginx.v2                     helm.sh/release.v1                 1      104d

These secrets contain the history of your Helm release. Checking the release secrets is a critical step in understanding how Helm manages release history and how we can manipulate it to reproduce the issue. Helm stores the details of each release, including the chart, values, and other metadata, as Kubernetes secrets. These secrets are named in a specific format: sh.helm.release.v1.<release-name>.v<revision-number>. The helm.sh/release.v1 annotation indicates that the secret is a Helm release secret. By listing the secrets in the kube-system namespace and filtering the output using grep ingress and grep helm.release, we can identify the secrets associated with the ingress-nginx release. The output will show a list of secrets, each representing a revision of the release. The revision number is indicated by the .v<revision-number> suffix in the secret name. For example, sh.helm.release.v1.rke2-ingress-nginx.v1 represents the first revision of the rke2-ingress-nginx release, and sh.helm.release.v1.rke2-ingress-nginx.v2 represents the second revision. The number of secrets you see will depend on how many times you have deployed or upgraded the release. Each time you run helm install or helm upgrade, a new revision secret is created. By examining these secrets, we can see the history of the release and understand which revisions are available. This information is essential for reproducing the issue, as we will be deleting the latest release secret to create a superseded state. Deleting a release secret is a destructive operation that can lead to inconsistencies in the Helm release history. When a release secret is deleted, Helm loses track of the corresponding revision, which can cause issues with upgrades, rollbacks, and other operations. In our case, we are intentionally deleting the latest release secret to simulate a scenario where the release history is corrupted. This will allow us to observe how the helm-install pod behaves when it encounters a superseded state. So, by checking the release secrets, we gain a clear understanding of the Helm release history and identify the specific secret that we need to delete to reproduce the issue. This step is crucial for ensuring that we are manipulating the release history in a controlled manner and that we can accurately observe the helm-install pod's behavior.

Step 6: Delete the Latest Release Secret

This is the crucial step! Delete the secret corresponding to the latest release revision. Make sure to back it up first if you want to restore it later! In our example, we'll delete sh.helm.release.v1.rke2-ingress-nginx.v2:

kubectl delete secret -n kube-system sh.helm.release.v1.rke2-ingress-nginx.v2

Deleting the latest release secret is the key step in creating the superseded state that triggers the issue. By removing the secret that contains the most recent revision of the Helm release, we effectively break the chain of history and leave Helm in a state where it cannot accurately determine the current state of the deployment. This is analogous to removing the latest chapter from a book, leaving the reader with an incomplete story. The kubectl delete secret command is a powerful tool that allows you to remove secrets from your Kubernetes cluster. However, it's important to use this command with caution, as deleting secrets can have significant consequences, especially if the secrets contain sensitive information or are critical for the operation of your applications. In our case, we are intentionally deleting a release secret to reproduce a specific issue, but in a production environment, you should only delete secrets if you are absolutely sure that it is safe to do so. Before deleting the secret, it's highly recommended to back it up. This will allow you to restore the secret if necessary, mitigating the risk of data loss or application downtime. You can back up the secret by exporting it to a YAML file using the kubectl get secret command with the -o yaml option. For example, to back up the sh.helm.release.v1.rke2-ingress-nginx.v2 secret, you can run the following command:

kubectl get secret -n kube-system sh.helm.release.v1.rke2-ingress-nginx.v2 -o yaml > rke2-ingress-nginx.v2.yaml

This will create a YAML file named rke2-ingress-nginx.v2.yaml that contains the contents of the secret. You can then store this file in a safe location, such as a Git repository or a dedicated backup server. Once you have backed up the secret, you can proceed with deleting it using the kubectl delete secret command. After deleting the secret, Helm will no longer be able to retrieve the latest revision of the release. This will cause the release to enter a superseded state, which is the condition that we are trying to create. The superseded state will trigger the helm-install pod to attempt a fresh installation, which will fail because the release name is already in use. This failure will lead to the crash loop that we are investigating. So, deleting the latest release secret is a critical step in reproducing the issue, but it's important to do it with caution and to back up the secret first to mitigate the risk of data loss. This controlled manipulation of the release history allows us to observe the helm-install pod's behavior in a specific scenario and understand the root cause of the problem.

Step 7: Check Helm Again

Now, check the Helm status again:

helm ls -n kube-system | grep ingress

The status should now show superseded:

NAME                    NAMESPACE       REVISION        UPDATED                                 STATUS          CHART                           APP VERSION
rke2-ingress-nginx      kube-system     2               2023-10-27 14:30:00.123456789 +0000 UTC superseded      ingress-nginx-4.5.2             1.9.0

This confirms that deleting the secret has indeed put the release into a superseded state. Checking the Helm status after deleting the latest release secret is essential to confirm that we have successfully created the superseded state. As we discussed earlier, the superseded state occurs when Helm is aware of a release but cannot find the latest revision secret. This can happen due to various reasons, such as accidental deletion of secrets, manual intervention, or issues with the underlying storage system. In our case, we intentionally deleted the latest release secret to simulate this scenario. The helm ls command, as we used before, provides a summary of the Helm releases in a specified namespace. By running this command again after deleting the secret, we can observe the change in the release status. The STATUS column should now show superseded for the ingress-nginx release, indicating that Helm has detected the missing secret and has marked the release as superseded. If the status does not change to superseded, it could indicate that there is a problem with the way you deleted the secret or that there is another issue preventing Helm from detecting the change. In this case, you should double-check the steps you followed and examine the Helm controller logs for any error messages. The fact that the status has changed to superseded confirms that we have successfully manipulated the release history and created the condition that we want to investigate. This is a critical milestone in reproducing the issue, as we now have a Helm release in a state that is known to cause problems with the helm-install pod. The superseded state is not necessarily an error in itself. It simply indicates that the latest revision of the release is not available. However, it can become a problem if the helm-install pod or other controllers are not designed to handle this state gracefully. As we will see in the next steps, the helm-install pod's inability to handle the superseded state is what leads to the crash loop that we are investigating. So, by checking the Helm status and confirming that the release is in a superseded state, we set the stage for observing the helm-install pod's behavior and understanding the root cause of the issue.

Step 8: Change the HelmChartConfig

Now, let's trigger an update. Modify the HelmChartConfig by changing a value. For example, change the foo label:

apiVersion: helm.cattle.io/v1
kind: HelmChartConfig
metadata:
  name: rke2-ingress-nginx
  namespace: kube-system
spec:
  valuesContent: |-
    controller:
      metrics:
        enabled: true
        serviceMonitor:
          enabled: true
          additionalLabels:
            foo: "bar2"

Apply this change to your cluster. Changing the HelmChartConfig is the action that triggers the helm-install pod to attempt an update of the Helm release. This is a crucial step in reproducing the issue, as it allows us to observe how the pod behaves when it encounters a superseded state and attempts to reconcile the release. The HelmChartConfig resource, as we discussed earlier, is a declarative way to manage Helm charts in Kubernetes. By modifying the valuesContent field, we are essentially changing the desired state of the release. This change will be detected by the Helm controller, which will then initiate an update of the release. The update process typically involves fetching the latest version of the chart, applying the new values, and deploying the updated release to the cluster. However, in our case, the release is in a superseded state because we deleted the latest release secret. This means that the Helm controller will not be able to retrieve the latest revision of the release and will encounter an error when it attempts to perform the update. The specific error that the controller encounters will depend on how it is designed to handle superseded releases. In the case of the helm-install pod, as we will see in the next steps, it falls back to the helm install command, which is not designed to handle updates of existing releases. This leads to the