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Added explanation of alpha non-preempting PriorityClasses to the "Pod Priority and Preemption" doc. (#14599)

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Vallery Lancey 2019-06-10 17:54:15 -07:00 committed by Kubernetes Prow Robot
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content/en/docs/concepts/configuration/pod-priority-preemption.md
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@ -77,6 +77,13 @@ when a cluster is under resource pressure. For this reason, it is not
recommended to disable preemption. recommended to disable preemption.
{{< /note >}} {{< /note >}}
{{< note >}}
In Kubernetes 1.15 and later,
if the feature `NonPreemptingPriority` is enabled,
PriorityClasses have the option to set `preemptionPolicy: Never`.
This will prevent pods of that PriorityClass from preempting other pods.
{{< /note >}}
In Kubernetes 1.11 and later, preemption is controlled by a kube-scheduler flag In Kubernetes 1.11 and later, preemption is controlled by a kube-scheduler flag
`disablePreemption`, which is set to `false` by default. `disablePreemption`, which is set to `false` by default.
If you want to disable preemption despite the above note, you can set If you want to disable preemption despite the above note, you can set
@ -145,6 +152,55 @@ globalDefault: false
description: "This priority class should be used for XYZ service pods only." description: "This priority class should be used for XYZ service pods only."
``` ```
### Non-preempting PriorityClasses (alpha) {#non-preempting-priority-class}
1.15 adds the `PreemptionPolicy` field as an alpha feature.
It is disabled by default in 1.15,
and requires the `NonPreemptingPriority`[feature gate](https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/
) to be enabled.
Pods with `PreemptionPolicy: Never` will be placed in the scheduling queue
ahead of lower-priority pods,
but they cannot preempt other pods.
A non-preempting pod waiting to be scheduled will stay in the scheduling queue,
until sufficient resources are free,
and it can be scheduled.
Non-preempting pods,
like other pods,
are subject to scheduler back-off.
This means that if the scheduler tries these pods and they cannot be scheduled,
they will be retried with lower frequency,
allowing other pods with lower priority to be scheduled before them.
Non-preempting pods may still be preempted by other,
high-priority pods.
`PreemptionPolicy` defaults to `PreemptLowerPriority`,
which will allow pods of that PriorityClass to preempt lower-priority pods
(as is existing default behavior).
If `PreemptionPolicy` is set to `Never`,
pods in that PriorityClass will be non-preempting.
An example use case is for data science workloads.
A user may submit a job that they want to be prioritized above other workloads,
but do not wish to discard existing work by preempting running pods.
The high priority job with `PreemptionPolicy: Never` will be scheduled
ahead of other queued pods,
as soon as sufficient cluster resources "naturally" become free.
#### Example Non-preempting PriorityClass
```yaml
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: high-priority-nonpreempting
value: 1000000
preemptionPolicy: Never
globalDefault: false
description: "This priority class will not cause other pods to be preempted."
```
## Pod priority ## Pod priority
After you have one or more PriorityClasses, you can create Pods that specify one After you have one or more PriorityClasses, you can create Pods that specify one