Debugging Kubernetes Flaky Test TestPlugin Resource Finalizer Prebind

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This article dives deep into a flaky test within the Kubernetes ecosystem, specifically focusing on TestPlugin/with-resources-finalizer-gets-added/prebind. We'll analyze the error, explore its reproducibility, and discuss potential causes and solutions. Guys, let's get started!

Understanding the Flaky Test

The flaky test in question is TestPlugin/with-resources-finalizer-gets-added/prebind, categorized under Kubernetes. It has been identified as a recurring issue in the ci-kubernetes-unit-1-34 job, as evident from the Test Grid link provided: https://testgrid.k8s.io/sig-release-1.34-blocking#ci-kubernetes-unit-1-34.

A specific flaky run can be examined at: https://prow.k8s.io/view/gs/kubernetes-ci-logs/logs/ci-kubernetes-unit-1-34/1955235500008673280. This run provides valuable insights into the failure scenario and the context in which it occurred. Analyzing these details is crucial for pinpointing the root cause of the flakiness. The test failure indicates an issue related to resource claim assumptions, specifically concerning the ResourceClaim object. The test expects a certain ResourceClaim configuration to be present but fails to find it, suggesting a discrepancy in how resources are being claimed or managed during the prebind phase. This could stem from various factors, including timing issues, race conditions, or incorrect state management within the dynamic resource allocation logic. Further investigation into the test setup and the dynamic resource plugin's behavior is warranted to identify the precise cause. Understanding the specifics of the ResourceClaim and its role in the test is essential for formulating a targeted solution.

Analyzing the Error

The test fails with a clear error message, which is a crucial starting point for debugging:

{Failed  === RUN   TestPlugin/with-resources-finalizer-gets-added/prebind
    dynamicresources_test.go:1826: Assumed claims are different, expected: &ResourceClaim{ObjectMeta:{my-pod-my-resource  default    0 0001-01-01 00:00:00 +0000 UTC <nil> <nil> map[] map[] [{v1 Pod my-pod 1234 0xc00055956f <nil>}] [resource.kubernetes.io/delete-protection] []},Spec:ResourceClaimSpec{Devices:DeviceClaim{Requests:[]DeviceRequest{DeviceRequest{Name:req-1,Exactly:&ExactDeviceRequest{DeviceClassName:my-resource-class,Selectors:[]DeviceSelector{},AllocationMode:ExactCount,Count:1,AdminAccess:nil,Tolerations:[]DeviceToleration{},Capacity:nil,},FirstAvailable:[]DeviceSubRequest{},},},Constraints:[]DeviceConstraint{},Config:[]DeviceClaimConfiguration{},},},Status:ResourceClaimStatus{Allocation:&AllocationResult{Devices:DeviceAllocationResult{Results:[]DeviceRequestAllocationResult{DeviceRequestAllocationResult{Request:req-1,Driver:some-driver,Pool:worker,Device:instance-1,AdminAccess:nil,Tolerations:[]DeviceToleration{},BindingConditions:[],BindingFailureConditions:[],ShareID:nil,ConsumedCapacity:map[QualifiedName]resource.Quantity{},},},Config:[]DeviceAllocationConfiguration{},},NodeSelector:&v11.NodeSelector{NodeSelectorTerms:[]NodeSelectorTerm{NodeSelectorTerm{MatchExpressions:[]NodeSelectorRequirement{},MatchFields:[]NodeSelectorRequirement{NodeSelectorRequirement{Key:metadata.name,Operator:In,Values:[worker],},},},},},AllocationTimestamp:<nil>,},ReservedFor:[]ResourceClaimConsumerReference{ResourceClaimConsumerReference{APIGroup:,Resource:pods,Name:my-pod,UID:1234,},},Devices:[]AllocatedDeviceStatus{},},} not found
--- FAIL: TestPlugin/with-resources-finalizer-gets-added/prebind (0.00s)

This error message indicates that the test expected a specific ResourceClaim object but did not find it. The ResourceClaim object's details, including its ObjectMeta, Spec, and Status, are printed in the error message. This allows for a precise comparison between the expected state and the actual state. Guys, the key here is that the test's assertion, located at https://github.com/kubernetes/kubernetes/blob/790393ae92e97262827d4f1fba24e8ae65bbada0/pkg/scheduler/framework/plugins/dynamicresources/dynamicresources_test.go#L1826, checks for the existence and correctness of this ResourceClaim. The error suggests that the ResourceClaim was either not created as expected or its state does not match the anticipated configuration. Further investigation into the test logic, particularly the prebind phase, is needed to determine why the ResourceClaim is not being found or is in an unexpected state. This involves examining the steps taken to create the ResourceClaim, the conditions under which it is expected to exist, and any potential race conditions or timing issues that might affect its availability. Understanding the flow of events leading up to the assertion failure is crucial for identifying the root cause of the problem.

The relevant code for this test can also be found at https://github.com/kubernetes/kubernetes/blob/790393ae92e97262827d4f1fba24e8ae65bbada0/pkg/scheduler/framework/plugins/dynamicresources/dynamicresources_test.go#L1939, providing context for the assertion failure.

Reproducing the Flaky Test

One of the most effective ways to understand a flaky test is to reproduce it reliably. The provided information indicates that the test can be reproduced using the stress tool. The following command was used:

$ go test -race ./pkg/scheduler/framework/plugins/dynamicresources/ -c
$ stress -p=32 ./dynamicresources.test -test.run="TestPlugin/with-resources-finalizer-gets-added"

This command first compiles the test with race condition detection enabled (go test -race). Then, it uses stress to run the test concurrently with 32 processes (-p=32). This approach effectively simulates a high-load environment, increasing the likelihood of exposing timing-related issues or race conditions. The -test.run flag specifies the particular test function to execute, in this case, TestPlugin/with-resources-finalizer-gets-added. By running the test under stress, we can observe how it behaves when multiple instances are competing for resources or attempting to modify shared state simultaneously. This often reveals subtle bugs or synchronization problems that are not apparent under normal testing conditions. The ability to reproduce the flakiness consistently is a significant step towards understanding the root cause and developing a robust fix. It allows developers to iterate on potential solutions and verify their effectiveness in a controlled and repeatable manner. Without consistent reproduction, it can be challenging to confirm that a fix truly addresses the underlying issue.

The results of running the stress test show that the test fails intermittently:

5s: 64 runs so far, 0 failures
10s: 165 runs so far, 0 failures
15s: 271 runs so far, 0 failures
20s: 367 runs so far, 0 failures
25s: 472 runs so far, 0 failures
...
10m55s: 13612 runs so far, 30 failures (0.22%)
11m0s: 13716 runs so far, 30 failures (0.22%)
11m5s: 13823 runs so far, 31 failures (0.22%)

This output indicates that the test fails approximately 0.22% of the time under stress. The ability to reproduce the failure, even at a relatively low rate, is crucial for debugging. This reproducible flakiness strongly suggests the presence of a race condition or timing-dependent issue. The fact that the test passes most of the time but fails intermittently under stress indicates that the failure is not due to a fundamental logic error but rather to a subtle interaction between concurrent operations. This could involve shared resources, asynchronous processes, or dependencies on external state. Identifying the specific point of contention requires careful analysis of the test code, the dynamic resource plugin's implementation, and the interactions between them. Techniques such as code reviews, debugging with race condition detectors, and adding logging or tracing can help pinpoint the exact sequence of events that leads to the failure. Once the root cause is identified, a fix can be implemented, such as adding appropriate synchronization mechanisms or modifying the code to be more resilient to timing variations.

Potential Causes and Solutions

Based on the error message and the reproducibility under stress, here are some potential causes for the flaky test:

  1. Race condition: A race condition might exist in the code that manages the ResourceClaim objects. Multiple goroutines might be trying to create, update, or delete the same ResourceClaim concurrently, leading to inconsistent state. This is a common cause of flakiness in concurrent tests. To address this, we need to carefully review the code that handles ResourceClaim objects and identify potential areas where concurrent access might occur. This could involve using locks or other synchronization primitives to protect shared data structures. Additionally, the test itself might need to be adjusted to ensure that it properly synchronizes with the operations it is testing. For example, the test might need to wait for a ResourceClaim to be created or updated before making assertions about its state. Thoroughly analyzing the code and the test logic for potential race conditions is crucial for resolving this type of flakiness.

  2. Timing issues: The test might be relying on a specific timing sequence, and under stress, these timings might be disrupted. For example, the test might be checking for a ResourceClaim before it has been fully created or propagated through the system. Timing issues can be particularly difficult to debug because they often depend on factors such as system load, network latency, and the scheduling of goroutines. To mitigate these issues, the test should avoid relying on specific timing sequences and instead use more robust synchronization mechanisms. This might involve waiting for events or using conditions to ensure that the system is in the expected state before proceeding. Additionally, the test environment can be controlled to minimize variations in timing, such as by running the test on a dedicated machine or by limiting the number of concurrent operations. Careful attention to timing and synchronization is essential for creating tests that are reliable and not prone to flakiness.

  3. Incorrect state management: The state of the ResourceClaim might not be correctly managed throughout the test. This could involve issues with how the ResourceClaim is created, updated, or deleted, leading to inconsistencies in its state. Incorrect state management can manifest in various ways, such as a ResourceClaim being created with incorrect parameters, not being updated when expected, or being deleted prematurely. To address this, the code that manages the ResourceClaim state needs to be carefully reviewed for any logical errors or inconsistencies. This includes the code that creates the ResourceClaim, the code that updates its fields, and the code that deletes it. Additionally, the test should verify that the ResourceClaim state is as expected at various points in the test execution. This can be done by adding assertions that check the ResourceClaim's fields and status. Ensuring correct state management is crucial for the reliability and correctness of the test.

To address these potential causes, the following steps can be taken:

  • Code review: Carefully review the code in dynamicresources_test.go and the surrounding code that manages ResourceClaim objects. Look for potential race conditions, timing issues, and incorrect state management.
  • Add logging: Add more logging to the test and the dynamic resource plugin to trace the creation, update, and deletion of ResourceClaim objects. This can help identify the exact sequence of events leading to the failure.
  • Use synchronization primitives: If race conditions are suspected, use locks or other synchronization primitives to protect shared data structures.
  • Improve test robustness: Make the test less reliant on specific timings by waiting for events or using conditions.
  • Debugging tools: Utilize debugging tools such as race condition detectors to identify and diagnose concurrency issues.

Conclusion

The flaky test TestPlugin/with-resources-finalizer-gets-added/prebind highlights the challenges of testing concurrent systems. By understanding the error message, reproducing the failure, and systematically investigating potential causes, we can work towards a solution. This analysis provides a solid foundation for further debugging and fixing the flakiness. Remember, guys, addressing flaky tests is crucial for maintaining the stability and reliability of Kubernetes!

  • What jobs are flaking due to the TestPlugin/with-resources-finalizer-gets-added/prebind test?
  • What is the error message for the flaky test TestPlugin/with-resources-finalizer-gets-added/prebind?
  • Where is the test assertion for the TestPlugin/with-resources-finalizer-gets-added/prebind test located?
  • How to reproduce the flaky test TestPlugin/with-resources-finalizer-gets-added/prebind?
  • What are the potential causes of the flaky test TestPlugin/with-resources-finalizer-gets-added/prebind?
  • What are the suggested solutions for the flaky test TestPlugin/with-resources-finalizer-gets-added/prebind?

Troubleshooting Kubernetes Flaky Test TestPlugin with Resources Finalizer Analysis and Solutions