Volcano Scheduler V1.12.0 Panic On Pod Scheduling

by Alex Johnson 50 views

Introduction: The Core of the Problem

Volcano scheduler v1.12.0 is experiencing a critical issue: a panic during pod scheduling. This problem arises when the scheduler is started without the --enable-metrics=true parameter. The observed behavior leads to a runtime error: invalid memory address or nil pointer dereference, indicating a serious flaw within the scheduling process. This article delves into the specifics of this issue, providing context, reproduction steps, and potential implications for users of Volcano.

The Heart of the Issue: Identifying the Root Cause

The core of the problem lies within the volcano-scheduler component, specifically during the phase where the scheduler attempts to place pods onto nodes. When the --enable-metrics=true flag is omitted, certain metrics-related functionalities might not be initialized correctly. This can cause the scheduler to malfunction, ultimately resulting in a nil pointer dereference. This is a common programming error that occurs when a program tries to access memory through a pointer that does not point to a valid memory address. In the context of the Volcano scheduler, this means that some critical data structures or objects are not properly initialized before being used, leading to the crash. The problem is pinpointed to commit 981e18b2, suggesting that a recent change introduced this regression.

Step-by-Step Reproduction: How to Trigger the Panic

To reproduce this issue, follow these steps:

  1. Start Volcano Without Metrics: Launch the Volcano scheduler without including the --enable-metrics=true parameter. This is the crucial step that sets the stage for the error.
  2. Deploy Pods: Submit some pods to the Kubernetes cluster. These pods will be scheduled by the Volcano scheduler.
  3. Observe the Panic: The Volcano scheduler will begin the process of scheduling the pods. At this stage, the scheduler may encounter the runtime error and panic.

By following these steps, you can directly observe the issue. The goal is to highlight the importance of the --enable-metrics=true flag.

Deep Dive: Expected vs. Actual Results

Expected Outcome

When deploying pods, the expected behavior is for the Volcano scheduler to allocate the pods to available nodes seamlessly. The scheduler should evaluate resource constraints, node availability, and other scheduling policies, eventually assigning each pod to a suitable node without any interruption or failure. This ensures that the applications running within the pods can function as expected.

Actual Outcome: The Scheduler's Breakdown

The actual outcome deviates significantly from the expected behavior. Instead of successfully scheduling the pods, the Volcano scheduler encounters a panic, reporting a runtime error: invalid memory address or nil pointer dereference. The scheduler terminates abruptly, preventing any further pod scheduling. This breaks the normal operation of the scheduling process and disrupts any workloads. This crash makes the cluster unusable for scheduling.

Details: Version and Context

This issue has been confirmed on Volcano v1.12.0. The context is critical here: this version of the Volcano scheduler is affected when started without enabling metrics. The inclusion of --enable-metrics=true might provide a temporary solution. Therefore, users operating in an environment without enabling metrics must take the appropriate steps to ensure the stability of the scheduling process.

Relevant Information

This section may include other information, such as logs from the scheduler. For instance, the stack trace indicates that the error originates in the k8s.io/kubernetes/pkg/scheduler/framework/plugins/interpodaffinity package. It suggests that there is an issue during the PreFilter stage within the InterPodAffinity plugin. This plugin is responsible for evaluating the affinity and anti-affinity rules among pods. In addition, the stack trace shows that the error occurs within the getExistingAntiAffinityCounts method, which is responsible for counting the anti-affinity relationships between pods. The absence of the --enable-metrics=true could lead to incorrect data structures or memory access, which triggers this error. The logs also show that the panic occurs in a goroutine, which means that the error occurs during a concurrent operation.

Conclusion: Troubleshooting and Recommendations

Addressing the Issue

To mitigate this problem, the primary recommendation is to always start the Volcano scheduler with the --enable-metrics=true parameter. This ensures that the metrics-related functionalities are properly initialized. If you are experiencing this issue, you should check your scheduler's deployment configuration to confirm that the metrics are enabled. In addition to enabling metrics, you might consider upgrading to a later version of Volcano. Make sure you check for any patches or updates.

Future Considerations

It is important to determine the root cause of the nil pointer dereference. This involves reviewing the code at the location identified in the stack trace, especially the parts related to the metrics and the InterPodAffinity plugin. Identifying and resolving the bug will help prevent the crash. Moreover, thorough testing, including the scenarios where metrics are disabled, will ensure that the scheduler will work in any environment. If the issue is persistent, consult the Volcano community forums or the project’s GitHub repository.

For more in-depth information on Kubernetes scheduling, consider exploring the official documentation and community resources. Here is a helpful link: