Revise DNS Horizontal Autoscaling task (#16069)
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Tim Bannister
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Kubernetes Prow Robot
Kubernetes Prow Robot
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@@ -4,28 +4,26 @@ content_template: templates/task
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---
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{{% capture overview %}}
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This page shows how to enable and configure autoscaling of the DNS service in a
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Kubernetes cluster.
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This page shows how to enable and configure autoscaling of the DNS service in
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your Kubernetes cluster.
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{{% /capture %}}
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{{% capture prerequisites %}}
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* {{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
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* This guide assumes your nodes use the AMD64 or Intel 64 CPU architecture
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* This guide assumes your nodes use the AMD64 or Intel 64 CPU architecture.
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* Make sure the [DNS feature](/docs/concepts/services-networking/dns-pod-service/) itself is enabled.
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* Kubernetes version 1.4.0 or later is recommended.
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* Make sure [Kubernetes DNS](/docs/concepts/services-networking/dns-pod-service/) is enabled.
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{{% /capture %}}
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{{% capture steps %}}
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## Determining whether DNS horizontal autoscaling is already enabled
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## Determine whether DNS horizontal autoscaling is already enabled {#determining-whether-dns-horizontal-autoscaling-is-already-enabled}
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List the {{< glossary_tooltip text="Deployments" term_id="deployment" >}}
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in your cluster in the kube-system namespace:
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in your cluster in the kube-system {{< glossary_tooltip text="namespace" term_id="namespace" >}}:
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```shell
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kubectl get deployment --namespace=kube-system
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@@ -42,12 +40,12 @@ If you see "dns-autoscaler" in the output, DNS horizontal autoscaling is
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already enabled, and you can skip to
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[Tuning autoscaling parameters](#tuning-autoscaling-parameters).
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## Getting the name of your DNS Deployment or ReplicationController
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## Get the name of your DNS Deployment {#find-scaling-target}
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List the Deployments in your cluster in the kube-system namespace:
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List the DNS deployments in your cluster in the kube-system namespace:
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```shell
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kubectl get deployment --namespace=kube-system
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kubectl get deployment -l k8s-app=kube-dns --namespace=kube-system
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```
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The output is similar to this:
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@@ -57,45 +55,31 @@ The output is similar to this:
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coredns 2 2 2 2 ...
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...
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In Kubernetes versions earlier than 1.12, the DNS Deployment was called "kube-dns".
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In Kubernetes versions earlier than 1.5 DNS was implemented using a
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ReplicationController instead of a Deployment. So if you don't see kube-dns,
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or a similar name, in the preceding output, list the ReplicationControllers in
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your cluster in the kube-system namespace:
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If you don't see a Deployment for DNS services, you can also look for it by name:
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```shell
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kubectl get rc --namespace=kube-system
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kubectl get deployment --namespace=kube-system
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```
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The output is similar to this:
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and look for a deployment named `coredns` or `kube-dns`.
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NAME DESIRED CURRENT READY AGE
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...
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kube-dns-v20 1 1 1 ...
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...
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## Determining your scale target
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If you have a DNS Deployment, your scale target is:
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Your scale target is
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Deployment/<your-deployment-name>
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where `<your-deployment-name>` is the name of your DNS Deployment. For example, if
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your DNS Deployment name is coredns, your scale target is Deployment/coredns.
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the name of your Deployment for DNS is coredns, your scale target is Deployment/coredns.
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If you have a DNS ReplicationController, your scale target is:
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{{< note >}}
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CoreDNS is the default DNS service for Kubernetes. CoreDNS sets the label
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`k8s-app=kube-dns` so that it can work in clusters that originally used
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kube-dns.
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{{< /note >}}
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ReplicationController/<your-rc-name>
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## Enable DNS horizontal autoscaling {#enablng-dns-horizontal-autoscaling}
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where `<your-rc-name>` is the name of your DNS ReplicationController. For example,
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if your DNS ReplicationController name is kube-dns-v20, your scale target is
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ReplicationController/kube-dns-v20.
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## Enabling DNS horizontal autoscaling
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In this section, you create a Deployment. The Pods in the Deployment run a
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In this section, you create a new Deployment. The Pods in the Deployment run a
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container based on the `cluster-proportional-autoscaler-amd64` image.
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Create a file named `dns-horizontal-autoscaler.yaml` with this content:
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@@ -117,7 +101,7 @@ The output of a successful command is:
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DNS horizontal autoscaling is now enabled.
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## Tuning autoscaling parameters
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## Tune DNS autoscaling parameters {#tuning-autoscaling-parameters}
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Verify that the dns-autoscaler {{< glossary_tooltip text="ConfigMap" term_id="configmap" >}} exists:
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@@ -148,7 +132,7 @@ Modify the fields according to your needs. The "min" field indicates the
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minimal number of DNS backends. The actual number of backends number is
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calculated using this equation:
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replicas = max( ceil( cores * 1/coresPerReplica ) , ceil( nodes * 1/nodesPerReplica ) )
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replicas = max( ceil( cores × 1/coresPerReplica ) , ceil( nodes × 1/nodesPerReplica ) )
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Note that the values of both `coresPerReplica` and `nodesPerReplica` are
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integers.
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@@ -242,22 +226,10 @@ the autoscaler Pod.
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* The autoscaler provides a controller interface to support two control
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patterns: *linear* and *ladder*.
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## Future enhancements
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Control patterns, in addition to linear and ladder, that consider custom metrics
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are under consideration as a future development.
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Scaling of DNS backends based on DNS-specific metrics is under consideration as
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a future development. The current implementation, which uses the number of nodes
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and cores in cluster, is limited.
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Support for custom metrics, similar to that provided by
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[Horizontal Pod Autoscaling](/docs/tasks/run-application/horizontal-pod-autoscale/),
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is under consideration as a future development.
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{{% /capture %}}
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{{% capture whatsnext %}}
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* Read about [Guaranteed Scheduling For Critical Add-On Pods](/docs/tasks/administer-cluster/guaranteed-scheduling-critical-addon-pods/).
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* Learn more about the
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[implementation of cluster-proportional-autoscaler](https://github.com/kubernetes-incubator/cluster-proportional-autoscaler).
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{{% /capture %}}
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