Kueue: Fixing JobSet Suspension In Non-Managed Namespaces

Hey there, Kubernetes enthusiasts! Today, we're diving deep into a peculiar behavior observed with Kueue, a popular job scheduling and management system for Kubernetes. We'll explore an issue where Kueue might unexpectedly suspend JobSets in namespaces it's not supposed to be managing. This can be a bit of a head-scratcher, especially when your JobSets are explicitly configured with suspend: false. Let's unpack what's happening, why it's happening, and how we can get things back on track. Our main keywords here are Kueue, JobSet, Kubernetes, and namespace management. We'll also touch upon configuration nuances and troubleshooting steps.

Understanding the Problem: The Unexpected Suspension

The core of the issue lies in a specific Kueue configuration where manageJobsWithoutQueueName: true is enabled, and managedJobsNamespaceSelector is set up to exclude certain namespaces. The problem arises when a JobSet is created in one of these excluded namespaces, say the test namespace. Despite the JobSet itself being configured with suspend: false, the individual jobs within that JobSet end up being suspended. This contradicts the user's expectation that Kueue should not interfere with workloads in namespaces explicitly marked as unmanaged. We observed that the jobs created by the JobSet report a Suspended status, and repeatedly cycle through Suspended and Resumed events, indicating an ongoing, albeit unintended, interaction with Kueue. It's important to note that in these scenarios, no other Kueue-specific resources, like Workloads, are being created, further highlighting that Kueue shouldn't be actively managing these jobs. The setup seems to trigger a conflict in Kueue's reconciliation logic, causing it to incorrectly apply its suspension policy to jobs it should be ignoring. This behavior can lead to disruptions in your batch processing pipelines, especially in environments where namespaces are dynamically managed or have specific isolation requirements. The goal is to ensure that Kueue respects the managedJobsNamespaceSelector precisely, preventing any unintended side effects on non-managed resources. We'll be exploring the nuances of this configuration and how it interacts with Kueue's internal workings to understand the root cause of this surprising behavior. The implications of this bug can range from minor inconveniences to significant operational issues, depending on the criticality of the batch jobs affected.

Diving into the Configuration: What's Causing the Conflict?

Let's dissect the configuration that leads to this peculiar behavior. The key settings in Kueue that seem to contribute to this problem are:

• manageJobsWithoutQueueName: true: This setting tells Kueue to consider and manage Jobs (and by extension, resources that create Jobs like JobSets) even if they don't have a queue.kueue.x-k8s.io/name annotation. This broadens Kueue's scope of control.
• managedJobsNamespaceSelector: This is where the exclusion logic resides. In the problematic scenario, it's configured using matchExpressions with an operator NotIn. The values provided are a list of namespaces that Kueue *should not* manage, such as kube-system, kueue-system, and importantly, our example's test namespace.

When a JobSet is created in the test namespace—a namespace explicitly listed in the exclusion values of managedJobsNamespaceSelector—Kueue's controller still seems to be attempting to manage the underlying Jobs. This suggests a potential logic flaw in how Kueue evaluates the managedJobsNamespaceSelector, especially when combined with manageJobsWithoutQueueName: true. It appears that even though the namespace is marked for exclusion, the controller might still be picking up the JobSet and its associated Jobs for management. The fact that the jobs are repeatedly suspended and resumed indicates that Kueue is detecting them, trying to apply its management logic (suspension, presumably due to some internal state or a misunderstanding of the selector), and then potentially Kubernetes or another controller reacting, leading to the resume events. This creates a cycle of interference that prevents the JobSet from running as intended. The interaction between these two settings is critical. If manageJobsWithoutQueueName is false, Kueue wouldn't even look at these jobs unless they had a queue annotation. However, with it set to true, Kueue becomes more proactive, and it's in this proactive mode that the namespace selector's exclusion logic appears to be failing. Reproducing this issue consistently involves setting up Kueue with these specific configurations and then deploying a JobSet in a namespace that should be ignored. The minimal reproduction steps involve just these configuration parameters and a simple JobSet definition. The events logged by the Kubernetes job controller, showing frequent suspensions and resumptions, are key indicators that something is actively trying to control the job's lifecycle, and Kueue is the prime suspect given the context.

What We Expect vs. What's Happening

Let's be clear about the expected behavior versus the observed reality. What we expect is straightforward: If a namespace is explicitly excluded by Kueue's managedJobsNamespaceSelector, Kueue should completely ignore any workloads created within that namespace, including JobSets and their associated Jobs. The setting manageJobsWithoutQueueName: true should only apply to namespaces that Kueue *is* supposed to manage. In essence, the managedJobsNamespaceSelector acts as a definitive gate, determining which namespaces fall under Kueue's purview for managing jobs that don't have explicit queue assignments. Therefore, when a JobSet is deployed in a namespace like test, which is configured to be *not* managed, we anticipate zero interaction from Kueue. The JobSet, with its suspend: false configuration, should proceed to create its jobs without any interference, and those jobs should run to completion according to their own specifications.

However, what's happening is quite the opposite. As detailed in the problem description, the JobSet in the test namespace, despite being set to suspend: false, has its underlying jobs repeatedly suspended by Kueue. The job events show a flurry of Suspended and Resumed messages originating from batch/job-kueue-controller. This constant oscillation suggests that Kueue is detecting the jobs, attempting to manage them (likely by suspending them), and then perhaps other controllers or Kueue itself, in a confused state, attempts to resume them. This cyclical behavior prevents the jobs from ever starting or completing successfully. The crucial point is that the managedJobsNamespaceSelector, which is designed to prevent this exact scenario, seems to be failing. This leads to unintended side effects, where Kueue's control plane injects itself into workflows it's explicitly told to ignore. This behavior is particularly problematic because it breaks the principle of least privilege and clear separation of concerns in Kubernetes. Users configure these selectors to maintain control over which parts of their cluster are managed by specific controllers, and when that mechanism fails, it erodes trust and predictability in the system. The logs clearly indicate an active, albeit incorrect, management attempt by Kueue, which is the core of the problem we need to address.

Reproducing the Issue: A Step-by-Step Guide

To help diagnose and fix this unexpected behavior in Kueue, let's walk through the steps to reproduce it. This minimal setup will allow developers and users to verify the issue and test potential solutions. The key here is the specific combination of Kueue configuration and the deployment of a JobSet in a non-managed namespace.

Step 1: Configure Kueue for Selective Namespace Management

First, you need to configure Kueue's behavior regarding which namespaces it manages. This is typically done via the Kueue deployment's configuration or a ConfigMap. The critical settings are:

```yaml manageJobsWithoutQueueName: true managedJobsNamespaceSelector: matchExpressions: - key: kubernetes.io/metadata.name operator: NotIn values: [ kube-system, kueue-system , test] ```

In this configuration:

• manageJobsWithoutQueueName: true: This enables Kueue to manage Jobs even if they lack the specific Kueue queue annotation.
• managedJobsNamespaceSelector: This uses a label selector to determine which namespaces Kueue *should* manage. The NotIn operator with the specified values means that Kueue will not manage jobs in the kube-system, kueue-system, or test namespaces. Any other namespace would be managed if it doesn't match these excluded labels.

Ensure your Kueue installation reflects this configuration. This setup is designed to isolate Kueue's control to specific namespaces while allowing it to manage unannotated jobs within those permitted namespaces.

Step 2: Create a JobSet in an Excluded Namespace

Next, we deploy a JobSet into the test namespace, which we've configured Kueue to ignore. Here’s a minimal JobSet definition:

```yaml apiVersion: jobset.x-k8s.io/v1alpha2 kind: JobSet metadata: name: sleep-job-x5ffx namespace: test spec: replicatedJobs: - groupName: default name: workers replicas: 1 template: spec: template: spec: containers: - name: sleep image: busybox command: ["sleep", "10s"] resources: requests: cpu: "1" memory: 200Mi - groupName: default name: driver replicas: 1 template: spec: template: spec: containers: - name: sleep image: busybox command: ["sleep", "10s"] resources: requests: cpu: "2" memory: 200Mi suspend: false ```

Apply this YAML to your cluster:

```bash kubectl apply -f your-jobset.yaml ```

Step 3: Observe the Behavior

After applying the JobSet, immediately check the status of the JobSet and its constituent Jobs in the test namespace:

```bash kubectl get jobset sleep-job-x5ffx -n test kubectl get job -n test ```

You should observe output similar to this:

``` NAME TERMINALSTATE RESTARTS COMPLETED SUSPENDED AGE sleep-job-x5ffx 0 false 16m ```

And for the jobs:

``` NAME STATUS COMPLETIONS DURATION AGE sleep-job-x5ffx-driver-0 Suspended 0/1 16m sleep-job-x5ffx-workers-0 Suspended 0/1 16m ```

The key indicator is that the individual Jobs are marked as Suspended, even though the parent JobSet is not, and the namespace is supposed to be excluded from Kueue's management.

Step 4: Inspect Job Events

To confirm Kueue's involvement, examine the events for the suspended jobs:

```bash kubectl describe job -n test sleep-job-x5ffx-driver-0 kubectl describe job -n test sleep-job-x5ffx-workers-0 ```

You will likely see events like:

``` Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Suspended 10m (x2 over 10m) job-controller Job suspended Normal Suspended 13s (x14709 over 10m) batch/job-kueue-controller Kueue managed child job suspended Normal Resumed 13s (x3203 over 10m) job-controller Job resumed ```

The presence of events from batch/job-kueue-controller, especially the frequent Suspended and Resumed cycles, clearly indicates that Kueue is attempting to manage these jobs despite the namespace selector configuration. This reproduction accurately captures the scenario where Kueue incorrectly influences JobSets in non-managed namespaces.

Root Cause Analysis: Where the Logic Falters

The root cause of this issue appears to stem from how Kueue processes workload management, particularly concerning the interaction between manageJobsWithoutQueueName and managedJobsNamespaceSelector. When manageJobsWithoutQueueName is set to true, Kueue's controllers become more aggressive in scanning and attempting to manage Jobs across the cluster. The intention behind managedJobsNamespaceSelector is to filter these scans, ensuring that Kueue only applies its control logic to Jobs residing in namespaces that match the selector criteria (or, in this case, don't match the exclusion criteria). However, in the described scenario, it seems that Kueue's reconciliation loop might be identifying the JobSet and its associated Jobs *before* or *during* the namespace filtering process, or the filtering logic itself is not robustly applied to all paths where job management is considered. A potential flaw could be in the way Kueue identifies jobs to manage. If it iterates through all namespaces and then filters, or if it uses informer-based mechanisms that might trigger events before the namespace filter is fully applied, it could lead to the controller acting on jobs in excluded namespaces. The constant suspension and resumption of jobs point towards a race condition or a continuous reconciliation cycle where Kueue attempts to suspend a job it shouldn't be managing, and then perhaps other Kubernetes mechanisms or even Kueue's own reaction to its own state leads to attempts to resume it. This cyclical behavior suggests that Kueue's controller is indeed aware of the jobs but is misinterpreting or improperly applying the namespace exclusion rules. Specifically, the logic that decides whether a Job (or a Job created by a higher-level construct like a JobSet) should be managed might not correctly honor the NotIn clause of the managedJobsNamespaceSelector when manageJobsWithoutQueueName is enabled. This could be due to how the controller fetches and processes objects, or a bug in the predicate logic that determines object relevance. Understanding the exact flow within Kueue's controller, from object discovery to the decision to suspend or manage a job, is crucial for pinpointing this bug. It's likely that the mechanism responsible for enforcing the namespace selector is bypassed or incorrectly evaluated in the specific case of Jobs created by JobSets when manageJobsWithoutQueueName is active.

The Fix: Refining Kueue's Namespace Filtering

The solution to this problem involves refining how Kueue enforces its managedJobsNamespaceSelector, particularly when manageJobsWithoutQueueName is enabled. The core idea is to ensure that the namespace exclusion logic is applied rigorously and early in the controller's processing pipeline. Here's how the fix should ideally work:

• Early Exit for Excluded Namespaces: When Kueue's controller processes any Job or workload that could potentially be managed (especially those without queue annotations), it must first check if the namespace of that workload is included in the set of managed namespaces as defined by managedJobsNamespaceSelector. If the namespace is explicitly excluded (e.g., via the NotIn operator), the controller should immediately exit its management logic for that specific workload, without attempting to suspend or modify it. This early exit prevents the controller from even considering jobs in non-managed namespaces.
• Robust Selector Evaluation: The evaluation of managedJobsNamespaceSelector needs to be robust. It should correctly interpret all operators (In, NotIn, Exists, DoesNotExist) and handle the combination of selectors effectively. When manageJobsWithoutQueueName: true, the controller should strictly adhere to the namespaces permitted by the selector. If a namespace is not explicitly allowed or is explicitly disallowed, Kueue should have no control over jobs within it.
• Contextual Management Decision: Kueue should make the decision to manage a job based on the context of its namespace and the JobSet's configuration. If the JobSet itself is in a namespace that Kueue is configured *not* to manage, Kueue should not proceed to manage any of the Jobs that the JobSet creates, regardless of whether those Jobs have queue annotations or not. The JobSet's namespace should be the primary filter.
• Correct Handling of JobSet-Created Jobs: Kueue's controller needs to be aware that Jobs created by constructs like JobSets should also be subject to the namespace filtering. The controller should not treat these jobs differently just because they are dynamically generated by a higher-level object, especially if the parent object (the JobSet) resides in a non-managed namespace.

Implementing these changes would involve modifying the relevant parts of the Kueue controller code that handle Job and Pod reconciliation. Specifically, the code responsible for deciding whether to apply suspension or other management actions needs to be updated to incorporate a strict namespace check against the managedJobsNamespaceSelector configuration *before* any modification actions are taken. This ensures that Kueue respects the user's explicit configuration for namespace management, preventing unintended interference with workloads in excluded namespaces. The goal is to make the namespace selector a hard gatekeeper, ensuring that Kueue's control logic is only ever applied within the designated boundaries.

Conclusion and Next Steps

We've explored a critical issue where Kueue incorrectly suspends JobSets and their associated jobs in namespaces that are explicitly configured to be excluded from its management. This behavior, triggered by the combination of manageJobsWithoutQueueName: true and a restrictive managedJobsNamespaceSelector, leads to unexpected disruptions and violates the intended separation of concerns within a Kubernetes cluster. The detailed reproduction steps and analysis point towards a flaw in how Kueue's controller enforces namespace filtering, causing it to interfere with workloads it should ignore.

The proposed fix involves strengthening Kueue's namespace filtering logic, ensuring an early exit for workloads in excluded namespaces and a strict adherence to the selector's rules. By refining how Kueue evaluates which namespaces and workloads fall under its control, we can restore predictability and reliability to batch job management.

Moving forward, it's crucial for the Kueue community to address this bug promptly. Users relying on precise namespace control will benefit significantly from a fix that ensures Kueue respects the managedJobsNamespaceSelector under all circumstances. This will enhance the robustness and trustworthiness of Kueue as a Kubernetes job scheduler.

For further insights into Kubernetes job management and scheduling, you can refer to the official Kubernetes documentation on Jobs. Additionally, for deeper understanding of Kueue's features and architecture, the official Kueue documentation is an excellent resource.