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131 lines
6.1 KiB
Markdown
131 lines
6.1 KiB
Markdown
<!-- BEGIN MUNGE: UNVERSIONED_WARNING -->
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<!-- BEGIN STRIP_FOR_RELEASE -->
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
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If you are using a released version of Kubernetes, you should
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refer to the docs that go with that version.
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<strong>
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The latest release of this document can be found
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[here](http://releases.k8s.io/release-1.1/docs/user-guide/horizontal-pod-autoscaler.md).
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Documentation for other releases can be found at
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[releases.k8s.io](http://releases.k8s.io).
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</strong>
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--
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<!-- END STRIP_FOR_RELEASE -->
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<!-- END MUNGE: UNVERSIONED_WARNING -->
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# Horizontal Pod Autoscaler
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This document describes the current state of Horizontal Pod Autoscaler in Kubernetes.
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<!-- BEGIN MUNGE: GENERATED_TOC -->
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- [Horizontal Pod Autoscaler](#horizontal-pod-autoscaler)
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- [What is Horizontal Pod Autoscaler?](#what-is-horizontal-pod-autoscaler)
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- [How does Horizontal Pod Autoscaler work?](#how-does-horizontal-pod-autoscaler-work)
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- [API Object](#api-object)
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- [Support for horizontal pod autoscaler in kubectl](#support-for-horizontal-pod-autoscaler-in-kubectl)
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- [Autoscaling during rolling update](#autoscaling-during-rolling-update)
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- [Further reading](#further-reading)
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<!-- END MUNGE: GENERATED_TOC -->
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## What is Horizontal Pod Autoscaler?
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Horizontal pod autoscaling allows the number of pods in a replication controller or deployment
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to scale automatically based on observed CPU utilization.
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It is a [beta](../api.md#api-versioning) feature in Kubernetes 1.1.
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The autoscaler is implemented as a Kubernetes API resource and a controller.
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The resource describes behavior of the controller.
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The controller periodically adjusts the number of replicas in a replication controller or deployment
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to match the observed average CPU utilization to the target specified by user.
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## How does Horizontal Pod Autoscaler work?
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The autoscaler is implemented as a control loop.
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It periodically queries CPU utilization for the pods it targets.
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(The period of the autoscaler is controlled by `--horizontal-pod-autoscaler-sync-period` flag of controller manager.
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The default value is 30 seconds).
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Then, it compares the arithmetic mean of the pods' CPU utilization with the target and adjust the number of replicas if needed.
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CPU utilization is the recent CPU usage of a pod divided by the sum of CPU requested by the pod's containers.
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Please note that if some of the pod's containers do not have CPU request set,
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CPU utilization for the pod will not be defined and the autoscaler will not take any action.
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Further details of the autoscaling algorithm are given [here](../design/horizontal-pod-autoscaler.md#autoscaling-algorithm).
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Autoscaler uses heapster to collect CPU utilization.
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Therefore, it is required to deploy heapster monitoring in your cluster for autoscaling to work.
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Autoscaler accesses corresponding replication controller or deployment by scale sub-resource.
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Scale is an interface which allows to dynamically set the number of replicas and to learn the current state of them.
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More details on scale sub-resource can be found [here](../design/horizontal-pod-autoscaler.md#scale-subresource).
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## API Object
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Horizontal pod autoscaler is a top-level resource in the Kubernetes REST API (currently in [beta](../api.md#api-versioning)).
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More details about the API object can be found at
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[HorizontalPodAutoscaler Object](../design/horizontal-pod-autoscaler.md#horizontalpodautoscaler-object).
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## Support for horizontal pod autoscaler in kubectl
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Horizontal pod autoscaler, like every API resource, is supported in a standard way by `kubectl`.
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We can create a new autoscaler using `kubectl create` command.
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We can list autoscalers by `kubectl get hpa` and get detailed description by `kubectl describe hpa`.
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Finally, we can delete an autoscaler using `kubectl delete hpa`.
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In addition, there is a special `kubectl autoscale` command that allows for easy creation of horizontal pod autoscaler.
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For instance, executing `kubectl autoscale rc foo --min=2 --max=5 --cpu-percent=80`
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will create an autoscaler for replication controller *foo*, with target CPU utilization set to `80%`
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and the number of replicas between 2 and 5.
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The detailed documentation of `kubectl autoscale` can be found [here](kubectl/kubectl_autoscale.md).
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## Autoscaling during rolling update
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Currently in Kubernetes, it is possible to perform a rolling update by managing replication controllers directly,
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or by using the deployment object, which manages the underlying replication controllers for you.
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Horizontal pod autoscaler only supports the latter approach: the horizontal pod autoscaler is bound to the deployment object,
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it sets the size for the deployment object, and the deployment is responsible for setting sizes of underlying replication controllers.
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Horizontal pod autoscaler does not work with rolling update using direct manipulation of replication controllers,
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i.e. you cannot bind a horizontal pod autoscaler to a replication controller and do rolling update (e.g. using `kubectl rolling-update`).
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The reason this doesn't work is that when rolling update creates a new replication controller,
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the horizontal pod autoscaler will not be bound to the new replication controller.
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## Further reading
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* Design documentation: [Horizontal Pod Autoscaling](../design/horizontal-pod-autoscaler.md).
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* Manual of autoscale command in kubectl: [kubectl autoscale](kubectl/kubectl_autoscale.md).
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* Usage example of [Horizontal Pod Autoscaler](horizontal-pod-autoscaling/README.md).
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<!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
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[]()
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<!-- END MUNGE: GENERATED_ANALYTICS -->
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