Add a section on interactions of Pod priority and QoS (#9715)

* Add a section on interactions of Pod priority and QoS * Copyedit
2018-08-03 10:10:20 -07:00
parent ab3fd0de7e
commit 5bcd5df3f3
1 changed files with 25 additions and 0 deletions
@@ -368,4 +368,29 @@ When multiple nodes exist for preemption and none of the above scenarios apply,
 we expect the scheduler to choose a node with the lowest priority. If that is
 not the case, it may indicate a bug in the scheduler.
 ## Interactions of Pod priority and QoS
 Pod priority and
 [QoS](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/node/resource-qos.md)
 are two orthogonal features with few interactions and no default restrictions on
 setting the priority of a Pod based on its QoS classes. The scheduler's
 preemption logic does consider QoS when choosing preemption targets. Preemption
 considers Pod priority and attempts to choose a set of targets with the lowest
 priority. Higher-priority Pods are considered for preemption only if the removal
 of the lowest priority Pods is not sufficient to allow the scheduler to schedule
 the preemptor Pod, or if the lowest priority Pods are protected by
 `PodDisruptionBudget`.
 The only component that considers both QoS and Pod priority is
 [Kubelet out-of-resource eviction](/docs/tasks/administer-cluster/out-of-resource/).
 The kubelet ranks Pods for eviction first by whether or not their usage of the
 starved resource exceeds requests, then by Priority, and then by the consumption
 of the starved compute resource relative to the Pods’ scheduling requests.
 See
 [Evicting end-user pods](/docs/tasks/administer-cluster/out-of-resource/#evicting-end-user-pods)
 for more details. Kubelet out-of-resource eviction does not evict Pods whose
 usage does not exceed their requests. If a Pod with lower priority is not
 exceeding its requests, it won't be evicted. Another Pod with higher priority
 that exceeds its requests may be evicted.
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