VictoriaMetrics Helm Chart Bug: Deprecated Metric Recording Rule
Introduction
This article addresses a bug encountered in the VictoriaMetrics Helm chart, specifically related to the recording rule for the deprecated metric scheduler_binding_duration_seconds_bucket. This issue, discovered in version v0.63.6 of the victoria-metrics-k8s-stack chart, triggers the RecordingRulesNoData alert due to the presence of recording rules that rely on metrics deprecated in Kubernetes 1.21. This article will delve into the details of the bug, its impact, the workaround implemented, and potential solutions for a more targeted fix. Understanding this issue is crucial for users of VictoriaMetrics in Kubernetes environments, as it can lead to unnecessary alerts and potentially obscure genuine issues. This article aims to provide a comprehensive overview of the problem and its resolution, ensuring that users can effectively manage their monitoring and alerting configurations.
Problem Description
The core issue lies in the inclusion of recording rules within the VictoriaMetrics Helm chart that reference metrics deprecated in Kubernetes 1.21. One such metric is scheduler_binding_duration_seconds_bucket. These rules, intended to monitor the Kubernetes scheduler, become problematic in newer Kubernetes versions where the deprecated metrics are no longer available. Consequently, the RecordingRulesNoData alert is triggered, indicating that the recording rules are not receiving any data. This can lead to alert fatigue and potentially mask other critical alerts. The user who reported this bug was running Kubernetes 1.34.1, highlighting that this issue affects users on relatively recent Kubernetes versions. The specific recording rules in question are located within the kube-scheduler.rules.yaml file in the Helm chart. The presence of these rules, designed for older Kubernetes versions, creates a conflict with the updated metric landscape of newer Kubernetes deployments. This discrepancy underscores the importance of maintaining up-to-date monitoring configurations that align with the evolving Kubernetes ecosystem. Failure to do so can result in inaccurate alerts and a compromised monitoring posture.
Impact of the Bug
The primary impact of this bug is the triggering of the RecordingRulesNoData alert. While this alert itself doesn't directly indicate a critical system failure, its persistent presence can be disruptive. Repeated alerts for the same issue can desensitize operators, making them more likely to overlook genuine problems. This phenomenon, known as alert fatigue, is a significant concern in monitoring and alerting systems. Furthermore, the unnecessary alerts can clutter dashboards and notification channels, making it harder to identify and respond to actual incidents. In this specific case, the alert is triggered because the recording rules are querying for metrics that no longer exist. While the system is functioning correctly, the alert gives the false impression of a problem. This can lead to wasted time and effort in investigating the alert, only to discover that it is a consequence of the deprecated metric. Therefore, addressing this bug is essential for maintaining a clean and effective monitoring environment.
Workaround
The initial workaround implemented by the user was to disable the kubeScheduler rules entirely by setting defaultRules.rules.kubeScheduler: false in the Helm chart values. This effectively prevents the installation of the problematic recording rules, thus resolving the RecordingRulesNoData alert. However, this approach is a broad solution that disables all Kubernetes scheduler-related recording rules, which may include rules that are still relevant and valuable. By disabling the entire set of rules, the user potentially loses visibility into certain aspects of scheduler performance. Additionally, the user had to manually delete the vm-victoria-metrics-k8s-stack-kube-scheduler.rules resource, indicating that the Helm chart doesn't automatically remove the rules when the configuration is changed. While this workaround addresses the immediate issue, it is not an ideal long-term solution due to its broad scope and the manual steps required. A more targeted approach is needed to address the specific deprecated metrics while preserving the functionality of other relevant recording rules. This highlights the need for a more refined solution that can selectively disable or update the problematic rules without sacrificing overall monitoring coverage.
Detailed Analysis
To understand the bug fully, it's essential to examine the specific recording rules causing the issue. The deprecated metric, scheduler_binding_duration_seconds_bucket, is used in rules designed to monitor the time it takes for the Kubernetes scheduler to bind pods to nodes. These metrics were part of the legacy scheduling metrics in Kubernetes and were replaced with more granular and informative metrics in Kubernetes 1.21. The recording rules in the VictoriaMetrics Helm chart, specifically those in kube-scheduler.rules.yaml, were not updated to reflect these changes. As a result, when VictoriaMetrics attempts to evaluate these rules in a Kubernetes 1.21+ environment, it finds that the metrics do not exist, leading to the RecordingRulesNoData alert. The alert itself is defined in vmalert.yaml, which checks for recording rules that haven't produced data within a certain period. The combination of outdated rules and the alert definition creates the problem. A proper solution would involve either updating the recording rules to use the new Kubernetes metrics or selectively disabling only the rules that rely on the deprecated metrics. This requires a deeper understanding of the available metrics and the desired monitoring outcomes. A more granular approach would ensure that only the problematic rules are addressed, minimizing the impact on overall monitoring coverage.
Potential Solutions
Several solutions can address this bug more effectively than the current workaround. The most direct approach is to update the recording rules in the Helm chart to use the replacement metrics introduced in Kubernetes 1.21. This would involve identifying the new metrics that provide equivalent information to scheduler_binding_duration_seconds_bucket and modifying the rules accordingly. This solution ensures that the monitoring of scheduler binding duration continues to function correctly in newer Kubernetes environments. Another approach is to selectively disable only the recording rules that use the deprecated metrics. This can be achieved by introducing a more granular configuration option in the Helm chart that allows users to disable specific rules rather than the entire kubeScheduler rule set. This provides greater flexibility and minimizes the impact on monitoring coverage. A third option is to introduce version-specific rules. The Helm chart could include different sets of rules based on the Kubernetes version. This would involve checking the Kubernetes version during the chart deployment and installing the appropriate ruleset. This approach ensures that the correct rules are used for each Kubernetes environment. Each of these solutions offers a more targeted and effective way to address the bug compared to disabling all kubeScheduler rules. The best solution will depend on the specific requirements and constraints of the environment.
Implementing a Targeted Fix
Implementing a targeted fix requires a multi-step approach. First, identify the specific recording rules that rely on the deprecated scheduler_binding_duration_seconds_bucket metric. These rules are located in the kube-scheduler.rules.yaml file within the Helm chart. Next, determine the equivalent metrics in Kubernetes 1.21+ that provide similar information. The Kubernetes documentation and community resources can be valuable in this step. Once the replacement metrics are identified, modify the recording rules to use these new metrics. This may involve updating the PromQL queries within the rules to reference the new metric names and labels. Alternatively, if updating the rules is not feasible, a configuration option can be added to selectively disable the problematic rules. This could involve adding a new field in the defaultRules.rules section of the Helm chart values, allowing users to disable specific rules by name. Finally, thoroughly test the changes in a staging environment to ensure that the fix works as expected and doesn't introduce any new issues. This testing should include verifying that the RecordingRulesNoData alert is no longer triggered and that the monitoring of scheduler binding duration is functioning correctly. A well-implemented targeted fix will address the bug effectively while minimizing the impact on overall monitoring coverage.
Conclusion
The bug in the VictoriaMetrics Helm chart, related to the deprecated scheduler_binding_duration_seconds_bucket metric, highlights the importance of maintaining up-to-date monitoring configurations in dynamic environments like Kubernetes. The initial workaround of disabling all kubeScheduler rules, while effective in resolving the RecordingRulesNoData alert, is a broad solution that can compromise monitoring coverage. A more targeted fix, such as updating the recording rules to use current metrics or selectively disabling problematic rules, is essential for a robust and accurate monitoring system. This article has provided a detailed analysis of the bug, its impact, and potential solutions, offering a roadmap for users to address this issue effectively. By implementing a targeted fix, users can ensure that their VictoriaMetrics monitoring remains accurate and reliable, minimizing alert fatigue and enabling timely responses to genuine incidents. Regularly reviewing and updating monitoring configurations is a crucial aspect of managing Kubernetes environments, ensuring that the monitoring system remains aligned with the evolving landscape of metrics and APIs.
For more information on VictoriaMetrics and Kubernetes monitoring, visit the official VictoriaMetrics documentation.
