website/content/en/docs/concepts/scheduling-eviction/pod-scheduling-readiness.md

title	content_type	weight
Pod Scheduling Readiness	concept	40

{{< feature-state for_k8s_version="v1.26" state="alpha" >}}

Pods were considered ready for scheduling once created. Kubernetes scheduler does its due diligence to find nodes to place all pending Pods. However, in a real-world case, some Pods may stay in a "miss-essential-resources" state for a long period. These Pods actually churn the scheduler (and downstream integrators like Cluster AutoScaler) in an unnecessary manner.

By specifying/removing a Pod's .spec.schedulingGates, you can control when a Pod is ready to be considered for scheduling.

Configuring Pod schedulingGates

The schedulingGates field contains a list of strings, and each string literal is perceived as a criteria that Pod should be satisfied before considered schedulable. This field can be initialized only when a Pod is created (either by the client, or mutated during admission). After creation, each schedulingGate can be removed in arbitrary order, but addition of a new scheduling gate is disallowed.

{{}} stateDiagram-v2 s1: pod created s2: pod scheduling gated s3: pod scheduling ready s4: pod running if: empty scheduling gates? state if <> [] --> s1 s1 --> if s2 --> if: scheduling gate removed if --> s2: no if --> s3: yes
s3 --> s4 s4 --> [] {{< /mermaid >}}

Usage example

To mark a Pod not-ready for scheduling, you can create it with one or more scheduling gates like this:

{{< codenew file="pods/pod-with-scheduling-gates.yaml" >}}

After the Pod's creation, you can check its state using:

kubectl get pod test-pod

The output reveals it's in SchedulingGated state:

NAME       READY   STATUS            RESTARTS   AGE
test-pod   0/1     SchedulingGated   0          7s

You can also check its schedulingGates field by running:

kubectl get pod test-pod -o jsonpath='{.spec.schedulingGates}'

The output is:

[{"name":"foo"},{"name":"bar"}]

To inform scheduler this Pod is ready for scheduling, you can remove its schedulingGates entirely by re-applying a modified manifest:

{{< codenew file="pods/pod-without-scheduling-gates.yaml" >}}

You can check if the schedulingGates is cleared by running:

kubectl get pod test-pod -o jsonpath='{.spec.schedulingGates}'

The output is expected to be empty. And you can check its latest status by running:

kubectl get pod test-pod -o wide

Given the test-pod doesn't request any CPU/memory resources, it's expected that this Pod's state get transited from previous SchedulingGated to Running:

NAME       READY   STATUS    RESTARTS   AGE   IP         NODE  
test-pod   1/1     Running   0          15s   10.0.0.4   node-2

Observability

The metric scheduler_pending_pods comes with a new label "gated" to distinguish whether a Pod has been tried scheduling but claimed as unschedulable, or explicitly marked as not ready for scheduling. You can use scheduler_pending_pods{queue="gated"} to check the metric result.

{{% heading "whatsnext" %}}

• Read the PodSchedulingReadiness KEP for more details