Troubleshooting Longhorn Volume Degradation LonghornVolumeStatusWarning Alert

by Sharif Sakr 78 views

Hey guys! We've got an alert about a degraded Longhorn volume, pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a, and we need to dive in to figure out what's going on. This article will break down the alert details, help you understand the potential issues, and guide you through troubleshooting steps.

Discussion category: AndreiGavriliu, homelab

Additional information: (Updated at 2025-07-27 21:13:31.812699715 +0000 UTC m=+2889148.245973314)

Understanding the Alert: Longhorn Volume Status Warning

Let's kick things off by understanding what this alert means. The core issue is that a Longhorn volume, specifically pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a, is in a Degraded state. This is a warning sign that needs our attention. When a Longhorn volume is degraded, it means that one or more of its replicas might be unavailable or unhealthy, which could lead to data unavailability or potential data loss if not addressed promptly. We need to ensure our data integrity and application availability.

To truly understand the scope of the issue, let's break down the key components of this alert. The alertname is LonghornVolumeStatusWarning, which clearly indicates the nature of the problem. The volume in question is pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a, and it's associated with the pvc (Persistent Volume Claim) kanister-pvc-w47cp in the pvc_namespace kasten-io. This tells us that this volume is being used by a Persistent Volume Claim within the Kasten namespace. Kasten is a popular data management platform for Kubernetes, often used for backups and restores, which makes this alert even more critical. If a volume used for backups is degraded, it could impact your disaster recovery strategy.

This alert originated from the longhorn-system namespace, which is where Longhorn itself runs. The node affected is hive04, and the alert was triggered by the longhorn-manager pod (longhorn-manager-bjfgq) running on that node. This gives us a specific location to start our investigation. The instance is 10.42.3.175:9500, and the alert was processed by the job longhorn-backend. The severity is marked as warning, which means it's not a critical alert yet, but it definitely needs to be addressed before it escalates to a more severe state. The Prometheus instance monitoring this is kube-prometheus-stack/kube-prometheus-stack-prometheus, which is part of the kube-prometheus-stack.

In essence, this alert is telling us that a Longhorn volume backing a Persistent Volume Claim in the Kasten namespace is having issues on node hive04. Let's dive deeper into the specifics to understand the potential causes and how to fix them.

Decoding Common Labels and Annotations

To effectively troubleshoot this alert, it's crucial to dissect the common labels and annotations provided. These metadata elements offer valuable context and can significantly narrow down the root cause of the problem. Let's break down each label and annotation to understand its significance.

Common Labels Explained

The common labels provide a structured view of the alert's context. Here's a breakdown of each one:

  • alertname: LonghornVolumeStatusWarning - As we discussed, this label confirms that the alert is specifically related to the status of a Longhorn volume.
  • container: longhorn-manager - This indicates that the alert originated from the longhorn-manager container, which is responsible for managing Longhorn volumes.
  • endpoint: manager - This likely refers to the specific endpoint within the longhorn-manager service that triggered the alert.
  • instance: 10.42.3.175:9500 - This is the specific instance of the Longhorn manager that raised the alert, identified by its IP address and port.
  • issue: Longhorn volume pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a is Degraded. - This is a crucial label as it directly states the problem: the volume is in a degraded state.
  • job: longhorn-backend - This specifies the Prometheus job that is monitoring Longhorn backend components.
  • namespace: longhorn-system - This confirms that the issue is within the Longhorn system namespace, which is where Longhorn components run.
  • node: hive04 - This pinpoints the specific Kubernetes node where the problem is occurring. This is extremely helpful for focusing our troubleshooting efforts.
  • pod: longhorn-manager-bjfgq - This is the specific Longhorn manager pod that triggered the alert. Knowing the pod can help in checking logs and resource utilization.
  • prometheus: kube-prometheus-stack/kube-prometheus-stack-prometheus - This indicates which Prometheus instance is monitoring the Longhorn cluster. If you have multiple Prometheus instances, this helps identify the source of the alert.
  • pvc: kanister-pvc-w47cp - This is the Persistent Volume Claim associated with the degraded volume. As mentioned earlier, this PVC belongs to the Kasten namespace, suggesting it's used for backup and restore operations.
  • pvc_namespace: kasten-io - This confirms the namespace of the PVC, which is Kasten's namespace.
  • service: longhorn-backend - This label indicates the Longhorn backend service involved in the alert.
  • severity: warning - As noted earlier, this indicates the alert's severity level, allowing you to prioritize your response.
  • volume: pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a - This is the identifier of the affected Longhorn volume.

Common Annotations Explained

Common annotations provide human-readable descriptions and summaries of the alert. Here's what the annotations tell us:

  • description: Longhorn volume pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a on hive04 is Degraded for more than 10 minutes. - This annotation gives us a more detailed explanation of the alert, stating that the volume has been degraded for over 10 minutes on node hive04. This duration is important because it helps us understand the urgency of the situation.
  • summary: Longhorn volume pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a is Degraded - This is a concise summary of the alert, making it easy to understand the core issue at a glance.

By thoroughly understanding these labels and annotations, we have a solid foundation for diagnosing the root cause of the degraded Longhorn volume. The fact that the volume has been degraded for more than 10 minutes suggests that this isn't a transient issue and requires immediate investigation. Now, let's move on to exploring the potential causes and troubleshooting steps.

Investigating the Alerts and Potential Causes

Now that we've deciphered the labels and annotations, let's dive into the actual alerts and what they might be telling us. We'll also explore potential causes for the degraded volume status.

Analyzing the Alert Details

The alert details show that the alert started at 2025-07-27 21:12:31.569 +0000 UTC. This is the timestamp when the Longhorn volume was first detected as degraded. The link provided, GeneratorURL, points to a Prometheus graph with the expression longhorn_volume_robustness == 2. This is a key piece of information. In Longhorn, the longhorn_volume_robustness metric indicates the health of a volume:

  • 0: Detached
  • 1: Healthy
  • 2: Degraded
  • 3: Faulted

So, the Prometheus graph is showing us the volumes with a robustness value of 2, which confirms that our volume, pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a, is indeed degraded. Clicking on this link and examining the graph in Prometheus can provide more insights into the volume's historical health and any recent changes in its status.

Potential Causes for Degraded Volume Status

Several factors could lead to a Longhorn volume being in a degraded state. Here are some of the most common causes:

  1. Replica Issues: This is the most frequent cause. A degraded volume typically means one or more of its replicas are unhealthy or unavailable. This could be due to:
    • Node Failure: If the node where a replica is running has failed or become unreachable, the replica will be marked as unavailable.
    • Disk Issues: Problems with the underlying storage (disk) on a node can cause replicas to fail.
    • Network Connectivity: Network issues between nodes can prevent replicas from communicating, leading to a degraded state.
    • Longhorn Bug or Error: In rare cases, a bug in Longhorn itself could cause a volume to be incorrectly marked as degraded.
  2. Resource Constraints: If the node or the Longhorn system is experiencing resource constraints (CPU, memory, disk space), it can impact the performance and health of the replicas.
  3. Longhorn Upgrade Issues: Sometimes, issues can arise during Longhorn upgrades, leading to volume degradation.
  4. Storage Overutilization: If the storage pool used by Longhorn is nearing full capacity, it can lead to performance issues and volume degradation.
  5. Application Issues: While less common, issues with the application using the volume (in this case, potentially Kasten) could indirectly cause the volume to become degraded.

Given that the volume is associated with Kasten, it's crucial to also consider if there might be any issues with backup or restore operations that could be impacting the volume's health.

Troubleshooting Steps: A Practical Guide

Now that we have a good understanding of the alert and the potential causes, let's outline a step-by-step approach to troubleshoot this issue. Here's a structured plan:

  1. Check Longhorn UI: The Longhorn UI is your first stop. Log in to the Longhorn UI and navigate to the Volumes section. Find the volume pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a and examine its details. The UI will show you the status of each replica, which node they are running on, and any error messages. This will often pinpoint the problematic replica(s).
  2. Inspect Node Status: Since the alert mentions node: hive04, it's crucial to check the status of this node. Use kubectl describe node hive04 to check the node's conditions, resource utilization, and any recent events. Look for issues like NodeDiskPressure, MemoryPressure, or other problems that could impact the Longhorn replicas.
  3. Examine Replica Logs: Once you've identified the problematic replica(s), check the logs for those replicas. You can find the pod names for the replicas in the Longhorn UI. Use kubectl logs <replica-pod-name> -n longhorn-system to view the logs. Look for error messages, warnings, or any clues that indicate why the replica is failing.
  4. Check Longhorn Manager Logs: Also, examine the logs for the Longhorn manager pod (longhorn-manager-bjfgq) on node hive04. This can provide insights into any management-level issues affecting the volume. Use kubectl logs longhorn-manager-bjfgq -n longhorn-system.
  5. Verify Network Connectivity: Ensure that there are no network issues between the nodes in your cluster, especially between the node where the degraded volume's replicas are running and other nodes. You can use tools like ping or traceroute to check network connectivity.
  6. Check Disk Usage: Use df -h on node hive04 to check disk usage. If the disk is nearing full capacity, it could be causing issues with the replicas. Also, check the storage pool usage in the Longhorn UI.
  7. Investigate Kasten: Since the PVC is associated with Kasten, check the Kasten logs and events for any errors or issues related to backups or restores. It's possible that a failed backup operation is causing the volume to be in a degraded state.
  8. Longhorn Events: Use kubectl get events -n longhorn-system to check for any Longhorn-related events that might provide clues about the volume's degradation.
  9. Prometheus Metrics: Return to the Prometheus graph (GeneratorURL) and explore other Longhorn-related metrics, such as longhorn_replica_rebuild_total and longhorn_replica_state, to get a broader view of the Longhorn cluster's health.

By systematically following these steps, you should be able to identify the root cause of the degraded Longhorn volume and take appropriate action to resolve it. In the next section, we'll discuss common solutions and how to implement them.

Solutions and Remediation Strategies for Degraded Longhorn Volumes

After thoroughly investigating the alert and identifying the root cause of the degraded Longhorn volume, it's time to implement solutions. The specific steps you take will depend on the underlying issue, but here are some common remediation strategies and solutions:

Common Solutions Based on Root Cause

  1. Replica Failures: If the issue stems from replica failures, here are some steps you can take:
    • Node Recovery: If a node has failed, the primary solution is to recover the node. Once the node is back online, Longhorn will automatically attempt to rebuild the replicas on that node.
    • Disk Issues: If a disk is failing, you'll need to replace the disk. After replacing the disk, Longhorn will automatically rebuild the replicas on the new disk. Make sure to properly configure the storage pool to use the new disk.
    • Manual Replica Rebuild: In some cases, you might need to manually trigger a replica rebuild. You can do this via the Longhorn UI. Navigate to the volume details, find the degraded replica, and select the option to rebuild it. Be aware that this process can be resource-intensive and may take some time, depending on the size of the volume and the available resources.
    • Replica Eviction: If a replica is stuck in a degraded state and not recovering, you can try evicting it. This will force Longhorn to create a new replica on a healthy node. You can evict replicas from the Longhorn UI or using kubectl commands.
  2. Resource Constraints: If resource constraints are the culprit:
    • Increase Resources: Add more CPU, memory, or disk space to the affected node(s). You might need to scale up the node size or add more nodes to your Kubernetes cluster.
    • Optimize Resource Usage: Review the resource requests and limits for your pods and adjust them as needed. Ensure that your applications are not consuming excessive resources.
    • Longhorn Settings: Check Longhorn's settings related to resource usage, such as the concurrent replica rebuild limit. Adjust these settings if necessary, but be cautious about making drastic changes without understanding the implications.
  3. Storage Overutilization: If the storage pool is nearing full capacity:
    • Add Storage: Expand the storage pool by adding more disks or increasing the size of existing disks. Longhorn will automatically detect the new storage and make it available.
    • Cleanup Old Snapshots: Delete old or unnecessary snapshots to free up space. Snapshots can consume a significant amount of storage, so regular cleanup is essential.
    • Increase Storage Pool Size: You can increase the default storage pool size in Longhorn's settings to prevent future overutilization.
  4. Network Issues: If network connectivity is the problem:
    • Diagnose Network: Use network troubleshooting tools like ping, traceroute, and tcpdump to identify network connectivity issues between nodes.
    • Firewall Rules: Check your firewall rules to ensure that traffic between nodes is allowed on the necessary ports for Longhorn communication.
    • DNS Resolution: Verify that DNS resolution is working correctly in your cluster.
  5. Kasten Issues: If Kasten-related problems are suspected:
    • Review Kasten Logs: Check the Kasten logs for errors or warnings related to backup and restore operations.
    • Kasten Configuration: Verify that Kasten is correctly configured and has sufficient resources to perform backups and restores.
    • Manual Intervention: In some cases, you might need to manually intervene in Kasten operations, such as retrying a failed backup or deleting a stuck restore.

Step-by-Step Remediation Process

Here's a general step-by-step process to remediate a degraded Longhorn volume:

  1. Identify the Root Cause: Use the troubleshooting steps outlined earlier to pinpoint the exact cause of the degradation.
  2. Implement the Appropriate Solution: Based on the root cause, implement the corresponding solution from the list above.
  3. Monitor the Volume: After implementing the solution, closely monitor the volume in the Longhorn UI to ensure it returns to a healthy state. Check the replica statuses and look for any further issues.
  4. Verify Data Integrity: Once the volume is healthy, verify the integrity of the data stored on it. This is especially important if the volume is used for critical applications or backups. For Kasten-related volumes, you might want to run a test restore to ensure the backups are valid.
  5. Document the Issue and Solution: Document the issue, the root cause, and the solution you implemented. This will help you in the future if a similar problem occurs.
  6. Proactive Measures: Consider implementing proactive measures to prevent similar issues in the future. This might include:
    • Regular Monitoring: Set up alerts and monitoring for Longhorn volumes, nodes, and storage pools.
    • Capacity Planning: Ensure that you have sufficient resources (CPU, memory, disk space) for your Longhorn cluster.
    • Regular Maintenance: Perform regular maintenance tasks, such as cleaning up old snapshots and upgrading Longhorn components.
    • Disaster Recovery Plan: Develop a disaster recovery plan that includes procedures for recovering from Longhorn volume failures.

By following these solutions and remediation strategies, you can effectively address degraded Longhorn volumes and ensure the reliability of your storage in your Kubernetes environment. Remember, proactive monitoring and maintenance are key to preventing these issues from occurring in the first place.

Conclusion: Ensuring Longhorn Volume Health and Stability

Alright, guys, we've covered a lot in this article! We started with an alert about a degraded Longhorn volume, pvc-36ce5220-0b6d-4a17-a49e-abf14e17004a, and we've gone through the process of understanding the alert, identifying potential causes, troubleshooting the issue, and implementing solutions. We've emphasized the importance of data integrity and application availability throughout this process.

Longhorn is a powerful and reliable storage solution for Kubernetes, but like any complex system, it requires careful monitoring and maintenance. When a Longhorn volume becomes degraded, it's a sign that something needs attention. By following a structured approach to troubleshooting, you can quickly identify the root cause and take appropriate action to restore the volume to a healthy state.

Key takeaways from this article include:

  • Understanding Alerts: It's crucial to understand the details of an alert, including the labels and annotations. These provide valuable context and help you narrow down the problem.
  • Troubleshooting Process: A systematic troubleshooting process is essential for identifying the root cause of the issue. Start with the Longhorn UI, check node and replica statuses, examine logs, and verify network connectivity and disk usage.
  • Common Solutions: Common solutions for degraded Longhorn volumes include recovering failed nodes, rebuilding replicas, adding storage, resolving network issues, and addressing resource constraints.
  • Proactive Measures: Proactive monitoring, capacity planning, and regular maintenance are key to preventing Longhorn volume issues from occurring in the first place.
  • Kasten Integration: If you're using Longhorn with Kasten for backups and restores, it's important to also investigate Kasten-related issues that could impact volume health.

By diligently monitoring your Longhorn volumes and implementing these best practices, you can ensure the stability and reliability of your storage infrastructure. Remember, a healthy Longhorn cluster translates to healthy applications and data.

If you encounter a Longhorn volume degradation alert, don't panic! Follow the steps outlined in this article, and you'll be well-equipped to tackle the issue head-on. And as always, keep learning and stay proactive in managing your Kubernetes storage!