257 lines
10 KiB
Markdown
257 lines
10 KiB
Markdown
---
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title: Scheduler Configuration
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content_type: concept
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weight: 20
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---
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{{< feature-state for_k8s_version="v1.19" state="beta" >}}
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You can customize the behavior of the `kube-scheduler` by writing a configuration
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file and passing its path as a command line argument.
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<!-- overview -->
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<!-- body -->
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A scheduling Profile allows you to configure the different stages of scheduling
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in the {{< glossary_tooltip text="kube-scheduler" term_id="kube-scheduler" >}}.
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Each stage is exposed in a extension point. Plugins provide scheduling behaviors
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by implementing one or more of these extension points.
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You can specify scheduling profiles by running `kube-scheduler --config <filename>`,
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using the
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[KubeSchedulerConfiguration (v1beta1)](/docs/reference/config-api/kube-scheduler-config.v1beta1/)
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struct.
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A minimal configuration looks as follows:
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```yaml
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apiVersion: kubescheduler.config.k8s.io/v1beta1
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kind: KubeSchedulerConfiguration
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clientConnection:
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kubeconfig: /etc/srv/kubernetes/kube-scheduler/kubeconfig
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```
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## Profiles
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A scheduling Profile allows you to configure the different stages of scheduling
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in the {{< glossary_tooltip text="kube-scheduler" term_id="kube-scheduler" >}}.
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Each stage is exposed in an [extension point](#extension-points).
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[Plugins](#scheduling-plugins) provide scheduling behaviors by implementing one
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or more of these extension points.
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You can configure a single instance of `kube-scheduler` to run
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[multiple profiles](#multiple-profiles).
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### Extension points
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Scheduling happens in a series of stages that are exposed through the following
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extension points:
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1. `QueueSort`: These plugins provide an ordering function that is used to
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sort pending Pods in the scheduling queue. Exactly one queue sort plugin
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may be enabled at a time.
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1. `PreFilter`: These plugins are used to pre-process or check information
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about a Pod or the cluster before filtering. They can mark a pod as
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unschedulable.
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1. `Filter`: These plugins are the equivalent of Predicates in a scheduling
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Policy and are used to filter out nodes that can not run the Pod. Filters
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are called in the configured order. A pod is marked as unschedulable if no
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nodes pass all the filters.
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1. `PreScore`: This is an informational extension point that can be used
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for doing pre-scoring work.
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1. `Score`: These plugins provide a score to each node that has passed the
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filtering phase. The scheduler will then select the node with the highest
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weighted scores sum.
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1. `Reserve`: This is an informational extension point that notifies plugins
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when resources have been reserved for a given Pod. Plugins also implement an
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`Unreserve` call that gets called in the case of failure during or after
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`Reserve`.
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1. `Permit`: These plugins can prevent or delay the binding of a Pod.
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1. `PreBind`: These plugins perform any work required before a Pod is bound.
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1. `Bind`: The plugins bind a Pod to a Node. Bind plugins are called in order
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and once one has done the binding, the remaining plugins are skipped. At
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least one bind plugin is required.
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1. `PostBind`: This is an informational extension point that is called after
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a Pod has been bound.
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For each extension point, you could disable specific [default plugins](#scheduling-plugins)
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or enable your own. For example:
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```yaml
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apiVersion: kubescheduler.config.k8s.io/v1beta1
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kind: KubeSchedulerConfiguration
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profiles:
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- plugins:
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score:
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disabled:
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- name: NodeResourcesLeastAllocated
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enabled:
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- name: MyCustomPluginA
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weight: 2
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- name: MyCustomPluginB
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weight: 1
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```
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You can use `*` as name in the disabled array to disable all default plugins
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for that extension point. This can also be used to rearrange plugins order, if
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desired.
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### Scheduling plugins
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1. `UnReserve`: This is an informational extension point that is called if
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a Pod is rejected after being reserved and put on hold by a `Permit` plugin.
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## Scheduling plugins
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The following plugins, enabled by default, implement one or more of these
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extension points:
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- `SelectorSpread`: Favors spreading across nodes for Pods that belong to
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{{< glossary_tooltip text="Services" term_id="service" >}},
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{{< glossary_tooltip text="ReplicaSets" term_id="replica-set" >}} and
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{{< glossary_tooltip text="StatefulSets" term_id="statefulset" >}}.
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Extension points: `PreScore`, `Score`.
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- `ImageLocality`: Favors nodes that already have the container images that the
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Pod runs.
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Extension points: `Score`.
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- `TaintToleration`: Implements
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[taints and tolerations](/docs/concepts/scheduling-eviction/taint-and-toleration/).
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Implements extension points: `Filter`, `Prescore`, `Score`.
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- `NodeName`: Checks if a Pod spec node name matches the current node.
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Extension points: `Filter`.
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- `NodePorts`: Checks if a node has free ports for the requested Pod ports.
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Extension points: `PreFilter`, `Filter`.
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- `NodePreferAvoidPods`: Scores nodes according to the node
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{{< glossary_tooltip text="annotation" term_id="annotation" >}}
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`scheduler.alpha.kubernetes.io/preferAvoidPods`.
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Extension points: `Score`.
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- `NodeAffinity`: Implements
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[node selectors](/docs/concepts/scheduling-eviction/assign-pod-node/#nodeselector)
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and [node affinity](/docs/concepts/scheduling-eviction/assign-pod-node/#node-affinity).
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Extension points: `Filter`, `Score`.
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- `PodTopologySpread`: Implements
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[Pod topology spread](/docs/concepts/workloads/pods/pod-topology-spread-constraints/).
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Extension points: `PreFilter`, `Filter`, `PreScore`, `Score`.
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- `NodeUnschedulable`: Filters out nodes that have `.spec.unschedulable` set to
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true.
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Extension points: `Filter`.
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- `NodeResourcesFit`: Checks if the node has all the resources that the Pod is
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requesting.
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Extension points: `PreFilter`, `Filter`.
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- `NodeResourcesBalancedAllocation`: Favors nodes that would obtain a more
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balanced resource usage if the Pod is scheduled there.
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Extension points: `Score`.
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- `NodeResourcesLeastAllocated`: Favors nodes that have a low allocation of
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resources.
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Extension points: `Score`.
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- `VolumeBinding`: Checks if the node has or if it can bind the requested
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{{< glossary_tooltip text="volumes" term_id="volume" >}}.
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Extension points: `PreFilter`, `Filter`, `Reserve`, `PreBind`, `Score`.
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{{< note >}}
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`Score` extension point is enabled when `VolumeCapacityPriority` feature is
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enabled. It prioritizes the smallest PVs that can fit the requested volume
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size.
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{{< /note >}}
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- `VolumeRestrictions`: Checks that volumes mounted in the node satisfy
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restrictions that are specific to the volume provider.
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Extension points: `Filter`.
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- `VolumeZone`: Checks that volumes requested satisfy any zone requirements they
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might have.
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Extension points: `Filter`.
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- `NodeVolumeLimits`: Checks that CSI volume limits can be satisfied for the
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node.
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Extension points: `Filter`.
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- `EBSLimits`: Checks that AWS EBS volume limits can be satisfied for the node.
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Extension points: `Filter`.
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- `GCEPDLimits`: Checks that GCP-PD volume limits can be satisfied for the node.
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Extension points: `Filter`.
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- `AzureDiskLimits`: Checks that Azure disk volume limits can be satisfied for
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the node.
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Extension points: `Filter`.
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- `InterPodAffinity`: Implements
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[inter-Pod affinity and anti-affinity](/docs/concepts/scheduling-eviction/assign-pod-node/#inter-pod-affinity-and-anti-affinity).
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Extension points: `PreFilter`, `Filter`, `PreScore`, `Score`.
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- `PrioritySort`: Provides the default priority based sorting.
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Extension points: `QueueSort`.
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- `DefaultBinder`: Provides the default binding mechanism.
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Extension points: `Bind`.
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- `DefaultPreemption`: Provides the default preemption mechanism.
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Extension points: `PostFilter`.
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You can also enable the following plugins, through the component config APIs,
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that are not enabled by default:
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- `NodeResourcesMostAllocated`: Favors nodes that have a high allocation of
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resources.
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Extension points: `Score`.
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- `RequestedToCapacityRatio`: Favor nodes according to a configured function of
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the allocated resources.
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Extension points: `Score`.
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- `CinderVolume`: Checks that OpenStack Cinder volume limits can be satisfied
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for the node.
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Extension points: `Filter`.
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- `NodeLabel`: Filters and / or scores a node according to configured
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{{< glossary_tooltip text="label(s)" term_id="label" >}}.
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Extension points: `Filter`, `Score`.
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- `ServiceAffinity`: Checks that Pods that belong to a
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{{< glossary_tooltip term_id="service" >}} fit in a set of nodes defined by
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configured labels. This plugin also favors spreading the Pods belonging to a
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Service across nodes.
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Extension points: `PreFilter`, `Filter`, `Score`.
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### Multiple profiles
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You can configure `kube-scheduler` to run more than one profile.
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Each profile has an associated scheduler name and can have a different set of
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plugins configured in its [extension points](#extension-points).
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With the following sample configuration, the scheduler will run with two
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profiles: one with the default plugins and one with all scoring plugins
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disabled.
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```yaml
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apiVersion: kubescheduler.config.k8s.io/v1beta1
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kind: KubeSchedulerConfiguration
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profiles:
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- schedulerName: default-scheduler
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- schedulerName: no-scoring-scheduler
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plugins:
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preScore:
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disabled:
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- name: '*'
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score:
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disabled:
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- name: '*'
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```
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Pods that want to be scheduled according to a specific profile can include
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the corresponding scheduler name in its `.spec.schedulerName`.
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By default, one profile with the scheduler name `default-scheduler` is created.
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This profile includes the default plugins described above. When declaring more
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than one profile, a unique scheduler name for each of them is required.
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If a Pod doesn't specify a scheduler name, kube-apiserver will set it to
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`default-scheduler`. Therefore, a profile with this scheduler name should exist
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to get those pods scheduled.
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{{< note >}}
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Pod's scheduling events have `.spec.schedulerName` as the ReportingController.
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Events for leader election use the scheduler name of the first profile in the
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list.
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{{< /note >}}
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{{< note >}}
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All profiles must use the same plugin in the QueueSort extension point and have
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the same configuration parameters (if applicable). This is because the scheduler
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only has one pending pods queue.
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{{< /note >}}
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## {{% heading "whatsnext" %}}
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* Read the [kube-scheduler reference](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-scheduler/)
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* Learn about [scheduling](/docs/concepts/scheduling-eviction/kube-scheduler/)
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* Read the [kube-scheduler configuration (v1beta1)](/docs/reference/config-api/kube-scheduler-config.v1beta1/) reference
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