AI/ML and complex batch workloads continue to push the boundaries of Kubernetes scheduling. Following the foundational workload-centric enhancements introduced in previous releases, Kubernetes v1.37 delivers the next major milestone in the Workload-Aware Scheduling (WAS) journey. In this release, the core Workload and PodGroup APIs—enabling gang scheduling—along with Workload-Aware Preemption (WAP) and shared DRA ResourceClaims for PodGroups, all graduate to Beta, solidifying their role in the Kubernetes ecosystem.

To address the hierarchical scheduling requirements of modern high-performance distributed workloads, v1.37 introduces the new CompositePodGroup API. This new API allows expressing multi-level topology constraints, gang scheduling, and preemption policies for complex, heterogeneous groups of Pods. Crucially, this architectural expansion unlocks native scheduling support for advanced workload structures commonly managed by higher-order extension APIs such as JobSet and LeaderWorkerSet (LWS).

Alongside these API additions, v1.37 focuses on streamlining adoption by introducing a new set of controller integration APIs and the workloadbuilder Go library. These provide standardized building blocks that significantly simplify how out-of-tree controllers can integrate with WAS capabilities. Utilizing these new tools, the native Job controller integration has been upgraded to fully consume the expanded WAS APIs—enabling advanced scheduling policies, flexible disruption modes, and topology-aware scheduling for standard batch workloads.

Gang scheduling and Workload / PodGroup APIs

Kubernetes v1.37 delivers a major milestone: Workload / PodGroup APIs and gang scheduling are officially graduating to Beta. This graduation signals that native, "all-or-nothing" scheduling for workloads is solidifying for wider adoption.

Key updates to the API and gang scheduling algorithm in this release include:

Beta graduation and API versioning changes

The core Workload and PodGroup APIs have been promoted to v1beta1, meaning they are now one step away from General Availability (GA). For early adopters who have been testing these features, take note of the alpha versioning transition: v1alpha2 has been entirely replaced by v1alpha3. This transition introduces breaking changes designed to clean up the API structure around disruptionMode.

Native PodGroup queueing

A significant under-the-hood improvement in v1.37 makes the PodGroup a first-class citizen in the scheduling queue. Previously, even if belonging to a PodGroup, all member Pods were queued individually. Now, only the top-level PodGroup object is queued. This ensures all Pods share the same queueing behavior and lays the groundwork for more advanced PodGroup queueing strategies in the future.

Dynamic elasticity with minCount mutability

In earlier iterations, the minCount field, which dictates the minimum number of Pods required to successfully schedule a PodGroup, was strictly immutable. In v1.37, minCount is now mutable. This API change unlocks flexibility for elastic workloads. Controllers can now dynamically adjust the minimum required size of a gang on the fly, allowing workloads to gracefully degrade or expand without interrupting already-scheduled Pods.

Workload-aware preemption

In Kubernetes v1.37 the separate WorkloadAwarePreemption feature gate for workload-aware preemption was merged into the GenericWorkload feature gate, becoming a core part of the gang scheduling effort.

While the core concepts of workload-aware preemption stay the same, there are some differences between the v1.36 and v1.37 releases:

Performance and optimality

To check whether a preemptor can fit in the cluster thanks to preemption, the scheduler simulates the removal of all potential victims and re-runs the scheduling algorithm. After that it tries to reprieve as many victims as possible. In the v1.36 release, the scheduling algorithm was run for each victim reprieval, verifying whether with the victim reprieved, the algorithm can still find a valid placement for the preemptor. In v1.37, the scheduling algorithm is run only once and the preemptor Pods are assumed based on its output. Later, the reprieval checks whether a victim can still run in its place with the preemptor assumed.

PodGroup as a victim

One of the limitations of v1.36 was the fact that the default preemption for single Pods was not aware of PodGroups and was not respecting their disruptionMode fields, allowing for disruption of single Pods even when the PodGroup had disruptionMode: {all: {}} set. Kubernetes v1.37 removes this limitation; the default preemption now respects the PodGroup disruptionMode field.

Rename of the disruptionMode fields

During the promotion of the API to Beta, the disruptionMode field was changed to decouple its naming from the PodGroup object, allowing consistent naming across PodGroups and CompositePodGroups. The modes changed as follows: PodGroup became all, and Pod became single.

Support for preemptionPolicy

In v1.36, the PodGroup does not have a preemptionPolicy field. The PodGroup can perform preemption as long as none of the Pods forming it has preemptionPolicy: Never set. In v1.37, when the PodGroupPreemptionPolicy feature gate is enabled, a PodGroup also has a preemptionPolicy field. It serves as an authoritative field for whether a PodGroup can perform preemption.

CompositePodGroup API

In Kubernetes v1.36, workload-aware scheduling established a clean separation between static workload templates (Workload) and runtime group state (PodGroup), but the supported scheduling policies were limited to a single, flat group. The CompositePodGroup API, introduced in Kubernetes v1.37, extends this model to support hierarchical scheduling requirements.

This API allows its consumers to express multi-level scheduling requirements by organizing a workload in a tree-shaped hierarchy consisting of CompositePodGroup and PodGroup objects. Each CompositePodGroup carries policies and constraints that apply to other groups (CompositePodGroups and/or PodGroups), similar to how PodGroups govern scheduling behavior for a flat group of Pods. The scheduler treats such a hierarchy as a single scheduling unit and aims to satisfy the requirements specified by every group within that hierarchy.

Defining a workload hierarchy

To express multi-level scheduling requirements, you define a hierarchy of templates in a Workload object. Controllers then create the corresponding CompositePodGroup and PodGroup objects from that hierarchy.

To support this, the Workload API is extended with the spec.compositePodGroupTemplates field. Each CompositePodGroupTemplate defines a template for a parent CompositePodGroup and directly nests the templates (podGroupTemplates and/or compositePodGroupTemplates) from which its child groups derive.

Below is a sample Workload object that defines a two-level template hierarchy:

apiVersion: scheduling.k8s.io/v1beta1 kind: Workload metadata:  name: example-workload  annotations:  kubernetes.io/description: "Two-level workload hierarchy requiring 4 worker Pods and 1 driver Pod to schedule together." spec:  compositePodGroupTemplates:  - name: workload-root  schedulingPolicy:  gang:  minGroupCount: 2  podGroupTemplates:  - name: workers  schedulingPolicy:  gang:  minCount: 4  - name: driver  schedulingPolicy:  gang:  minCount: 1

After creating example-workload, a controller can stamp out the corresponding runtime group objects from these templates:

  1. A root CompositePodGroup that references the workload-root template in example-workload and carries its group-level scheduling policy (gang scheduling with minGroupCount: 2):

    apiVersion: scheduling.k8s.io/v1alpha3 kind: CompositePodGroup metadata:  name: example-root-group  annotations:  kubernetes.io/description: "Root group coordinating gang scheduling across child worker and driver PodGroups." spec:  workloadRef:  workloadName: example-workload  templateName: workload-root  schedulingPolicy:  gang:  minGroupCount: 2

  2. Two child PodGroup objects (example-workload-workers and example-workload-driver) that reference their respective leaf templates in example-workload and link to the root group via parentCompositePodGroupName:

    apiVersion: scheduling.k8s.io/v1beta1 kind: PodGroup metadata:  name: example-workload-workers  annotations:  kubernetes.io/description: "Worker group requiring at least 4 Pods to be scheduled together." spec:  parentCompositePodGroupName: example-root-group  workloadRef:  workloadName: example-workload  templateName: workers  schedulingPolicy:  gang:  minCount: 4 --- apiVersion: scheduling.k8s.io/v1beta1 kind: PodGroup metadata:  name: example-workload-driver  annotations:  kubernetes.io/description: "Driver group requiring 1 Pod to schedule alongside the workers." spec:  parentCompositePodGroupName: example-root-group  workloadRef:  workloadName: example-workload  templateName: driver  schedulingPolicy:  gang:  minCount: 1

How multi-level gang scheduling works

To schedule a hierarchical workload, kube-scheduler evaluates the entire group tree as a unified scheduling unit:

  • Recursive evaluation: The scheduler traverses the hierarchy from the root CompositePodGroup down to the leaf PodGroup objects. At each level, a parent CompositePodGroup is considered schedulable only when its child groups satisfy its scheduling policy (for example, placing at least minGroupCount of child groups when using the gang policy), while each leaf PodGroup must satisfy its own Pod-level policy (for example, placing at least minCount of member Pods when using the gang policy).
  • All-or-nothing scheduling: Once a valid combination of child groups is found that satisfies the requirements of the root CompositePodGroup, the Pods across the entire hierarchy are scheduled and bound atomically. If the root group cannot satisfy its policy constraints, the entire hierarchy remains unschedulable and no Pods are bound, preventing partial deployments and deadlocks.

Workload-aware preemption for the CompositePodGroup API

Kubernetes v1.37 extends workload-aware preemption to support CompositePodGroup hierarchies as well. Specifically, if a CompositePodGroup cannot be scheduled due to insufficient capacity in the cluster, the scheduler can invoke preemption to evict lower-priority workloads in order to fit the Pods belonging to that CompositePodGroup.

A CompositePodGroup can be selected for preemption as well. To specify the desired behavior during preemption, workload owners can specify an appropriate disruptionMode in the CompositePodGroup spec:

  • single: Allows individual child groups within the CompositePodGroup to be preempted and disrupted independently. This is the behavior when disruptionMode is not set.
  • all: Enforces "all-or-nothing" disruption semantics across the entire CompositePodGroup hierarchy. If any Pod within the descendant subtree must be preempted, the scheduler evicts all Pods across the entire hierarchy together.

Topology-aware scheduling

In Kubernetes v1.37, topology-aware scheduling expands to support complex, multi-level workload hierarchies and delivers performance improvements for existing single-level deployments.

Multi-level topology-aware scheduling

In Kubernetes v1.36, we introduced foundational topology-aware scheduling, allowing you to define co-location constraints directly on a PodGroup. While effective for single-level groupings, complex distributed workloads—such as large-scale AI/ML training, JobSet deployments, or disaggregated inference via LeaderWorkerSet (LWS)—often require co-location across multiple levels of cluster infrastructure simultaneously.

For example, an entire workload may need to run within a single availability zone, while different parts of that workload (such as specific worker groups or driver processes) require strict co-location within specific server racks.

In Kubernetes v1.37, alongside the new CompositePodGroup API (scheduling.k8s.io/v1alpha3), topology-aware scheduling expands to support multi-level topology-aware scheduling. You can now express complex co-location requirements by specifying topology constraints at different levels of a group hierarchy.

Top-down topology constraint resolution

During hierarchical scheduling, the kube-scheduler resolves multi-level topology constraints in a top-down manner. Specifically, topology domains that are considered during the scheduling of a child group are confined within a topology domain that corresponds to the placement assumed by the parent group.

Configuration and runtime execution

Using the updated Workload API (scheduling.k8s.io/v1beta1), you can configure multi-level topology constraints directly within compositePodGroupTemplates. In the example below, the parent template constrains the overall workload to a single availability zone (topology.kubernetes.io/zone), while child templates for workers and driver constrain their respective Pods to server racks (topology.example.com/rack) within that selected zone:

apiVersion: scheduling.k8s.io/v1beta1 kind: Workload metadata:  name: multi-level-tas-workload  namespace: job-ns  annotations:  kubernetes.io/description: "Workload defining zone-level co-location for the root group and rack-level co-location for child groups." spec:  compositePodGroupTemplates:  - name: root  schedulingPolicy:  gang:  minGroupCount: 2  schedulingConstraints:  topology:  - key: topology.kubernetes.io/zone  podGroupTemplates:  - name: workers  schedulingPolicy:  gang:  minCount: 8  schedulingConstraints:  topology:  - key: topology.example.com/rack  - name: driver  schedulingPolicy:  gang:  minCount: 1  schedulingConstraints:  topology:  - key: topology.example.com/rack

When a controller creates an instance of this workload at runtime, it spawns the corresponding runtime objects from these templates:

  1. The root CompositePodGroup referencing the root template, carrying the availability zone topology constraint and the hierarchical gang scheduling policy.
  2. The two child PodGroup objects (tas-workload-workers and tas-workload-driver), each referencing the root CompositePodGroup as their parent group via the parentCompositePodGroupName spec field:
apiVersion: scheduling.k8s.io/v1alpha3 kind: CompositePodGroup metadata:  name: tas-workload-root  namespace: job-ns  annotations:  kubernetes.io/description: "Root group constraining the entire workload to a single availability zone." spec:  workloadRef:  workloadName: multi-level-tas-workload  templateName: root  schedulingPolicy:  gang:  minGroupCount: 2  schedulingConstraints:  topology:  - key: topology.kubernetes.io/zone --- apiVersion: scheduling.k8s.io/v1beta1 kind: PodGroup metadata:  name: tas-workload-workers  namespace: job-ns  annotations:  kubernetes.io/description: "Worker group requiring 8 Pods co-located within a single rack in the selected zone." spec:  parentCompositePodGroupName: tas-workload-root  workloadRef:  workloadName: multi-level-tas-workload  templateName: workers  schedulingPolicy:  gang:  minCount: 8  schedulingConstraints:  topology:  - key: topology.example.com/rack --- apiVersion: scheduling.k8s.io/v1beta1 kind: PodGroup metadata:  name: tas-workload-driver  namespace: job-ns  annotations:  kubernetes.io/description: "Driver group requiring 1 Pod placed in a rack within the selected zone." spec:  parentCompositePodGroupName: tas-workload-root  workloadRef:  workloadName: multi-level-tas-workload  templateName: driver  schedulingPolicy:  gang:  minCount: 1  schedulingConstraints:  topology:  - key: topology.example.com/rack

During scheduling, the scheduler evaluates multiple candidate availability zones across the cluster for tas-workload-root. For each candidate zone, it subdivides the nodes by rack topology to explore feasible rack placements for tas-workload-workers and tas-workload-driver strictly within that zone, systematically evaluating multiple combinations across available zones and racks before making a scheduling decision.

By allowing topology constraints to be modeled hierarchically, Kubernetes v1.37 provides a structured way to express multi-level co-location requirements across complex cluster infrastructures.

Performance improvements for single-level TAS

Alongside the Alpha introduction of multi-level hierarchies, Kubernetes v1.37 reduces the cost of placement evaluation for existing single-level topology-aware scheduling. We are continuously working to optimize the efficiency of placement evaluation algorithms in kube-scheduler and plan to deliver further performance improvements in future releases.

Controller Integration APIs

Kubernetes v1.37 introduces new standard building blocks so that every controller can expose the same scheduling primitives in their own APIs, and share the same logic for translating them into scheduling objects. These primitives express specific scheduling behaviors — such as policies or disruption logic — while leaving the field naming flexible for each controller. A prime example of this is the native Job controller, which we detail in the next section.

Types prefixed with WorkloadPodGroup describe a leaf group of Pods; types prefixed with WorkloadCompositePodGroup describe a group of groups. A controller embeds them verbatim into its own API, under whatever field name fits its domain:

  • WorkloadPodGroupSchedulingPolicy — either basic, meaning standard Pod-by-Pod scheduling, or gang with a minCount. The composite variant takes a minGroupCount instead.
  • WorkloadPodGroupSchedulingConstraints — the topology constraints (topology[].key) the group's Pods must be co-located within.
  • WorkloadPodGroupDisruptionMode — single or all, with the preemption semantics described earlier in this post.
  • WorkloadPodGroupResourceClaim — the ResourceClaims shared across the group.

Only the shapes are shared, so controllers retain full autonomy over how they name and nest these fields in their own APIs.

The workloadbuilder library turns that intent into the scheduling objects. A controller describes its workload as a tree of WorkloadItem nodes — a node with children compiles to a CompositePodGroupTemplate, a node without children to a PodGroupTemplate — and attaches its own defaults plus the user-supplied building blocks to each node. From there, Validate() reports problems back at the exact field path within the controller's own API, BuildWorkload() compiles the tree into a Workload, and NewPodGroup() and NewCompositePodGroup() stamp out the runtime group objects.

Validation is deny-by-default: a controller declares the policies and disruption modes it actually supports through AllowedPolicies and AllowedDisruptionModes, and anything outside those lists is rejected. Building blocks added in future releases therefore stay unavailable until a controller explicitly opts into them.

For hierarchical workloads where a parent controller owns the Workload and delegates group creation to its children, NewBuilderFromExistingWorkload lets a child materialize only its own PodGroup from the parent's Workload.

Neither the building blocks nor the library have a feature gate of their own; they become user-visible through whichever controller adopts them. The native Job controller is the first to do so, and we detail it in the next section.

Integration with the Job controller

Building upon the new controller integration APIs, the Job API now features an explicit .spec.scheduling field, so you can declare how a Job should be scheduled instead of relying on the Job...