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Revise DNS Horizontal Autoscaling task #16069

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Revise DNS Horizontal Autoscaling task #16069

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76 changes: 24 additions & 52 deletions content/en/docs/tasks/administer-cluster/dns-horizontal-autoscaling.md
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Original file line number Diff line number Diff line change
Expand Up @@ -4,28 +4,26 @@ content_template: templates/task
---

{{% capture overview %}}
This page shows how to enable and configure autoscaling of the DNS service in a
Kubernetes cluster.
This page shows how to enable and configure autoscaling of the DNS service in
your Kubernetes cluster.
{{% /capture %}}

{{% capture prerequisites %}}

* {{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}

* This guide assumes your nodes use the AMD64 or Intel 64 CPU architecture
* This guide assumes your nodes use the AMD64 or Intel 64 CPU architecture.

* Make sure the [DNS feature](/docs/concepts/services-networking/dns-pod-service/) itself is enabled.

* Kubernetes version 1.4.0 or later is recommended.
* Make sure [Kubernetes DNS](/docs/concepts/services-networking/dns-pod-service/) is enabled.

{{% /capture %}}

{{% capture steps %}}

## Determining whether DNS horizontal autoscaling is already enabled
## Determine whether DNS horizontal autoscaling is already enabled {#determining-whether-dns-horizontal-autoscaling-is-already-enabled}

List the {{< glossary_tooltip text="Deployments" term_id="deployment" >}}
in your cluster in the kube-system namespace:
in your cluster in the kube-system {{< glossary_tooltip text="namespace" term_id="namespace" >}}:

```shell
kubectl get deployment --namespace=kube-system
Expand All @@ -42,12 +40,12 @@ If you see "dns-autoscaler" in the output, DNS horizontal autoscaling is
already enabled, and you can skip to
[Tuning autoscaling parameters](#tuning-autoscaling-parameters).

## Getting the name of your DNS Deployment or ReplicationController
## Get the name of your DNS Deployment {#find-scaling-target}

List the Deployments in your cluster in the kube-system namespace:
List the DNS deployments in your cluster in the kube-system namespace:

```shell
kubectl get deployment --namespace=kube-system
kubectl get deployment -l k8s-app=kube-dns --namespace=kube-system
```

The output is similar to this:
Expand All @@ -57,45 +55,31 @@ The output is similar to this:
coredns 2 2 2 2 ...
...


In Kubernetes versions earlier than 1.12, the DNS Deployment was called "kube-dns".

In Kubernetes versions earlier than 1.5 DNS was implemented using a
ReplicationController instead of a Deployment. So if you don't see kube-dns,
or a similar name, in the preceding output, list the ReplicationControllers in
your cluster in the kube-system namespace:
If you don't see a Deployment for DNS services, you can also look for it by name:

```shell
kubectl get rc --namespace=kube-system
kubectl get deployment --namespace=kube-system
```

The output is similar to this:
and look for a deployment named `coredns` or `kube-dns`.

NAME DESIRED CURRENT READY AGE
...
kube-dns-v20 1 1 1 ...
...

## Determining your scale target

If you have a DNS Deployment, your scale target is:
Your scale target is

Deployment/<your-deployment-name>

where `<your-deployment-name>` is the name of your DNS Deployment. For example, if
your DNS Deployment name is coredns, your scale target is Deployment/coredns.

If you have a DNS ReplicationController, your scale target is:
the name of your Deployment for DNS is coredns, your scale target is Deployment/coredns.

ReplicationController/<your-rc-name>
{{< note >}}
CoreDNS is the default DNS service for Kubernetes. CoreDNS sets the label
`k8s-app=kube-dns` so that it can work in clusters that originally used
kube-dns.
{{< /note >}}

where `<your-rc-name>` is the name of your DNS ReplicationController. For example,
if your DNS ReplicationController name is kube-dns-v20, your scale target is
ReplicationController/kube-dns-v20.
## Enable DNS horizontal autoscaling {#enablng-dns-horizontal-autoscaling}

## Enabling DNS horizontal autoscaling

In this section, you create a Deployment. The Pods in the Deployment run a
In this section, you create a new Deployment. The Pods in the Deployment run a
container based on the `cluster-proportional-autoscaler-amd64` image.

Create a file named `dns-horizontal-autoscaler.yaml` with this content:
Expand All @@ -117,7 +101,7 @@ The output of a successful command is:

DNS horizontal autoscaling is now enabled.

## Tuning autoscaling parameters
## Tune DNS autoscaling parameters {#tuning-autoscaling-parameters}

Verify that the dns-autoscaler {{< glossary_tooltip text="ConfigMap" term_id="configmap" >}} exists:

Expand Down Expand Up @@ -148,7 +132,7 @@ Modify the fields according to your needs. The "min" field indicates the
minimal number of DNS backends. The actual number of backends number is
calculated using this equation:
replicas = max( ceil( cores * 1/coresPerReplica ) , ceil( nodes * 1/nodesPerReplica ) )
replicas = max( ceil( cores × 1/coresPerReplica ) , ceil( nodes × 1/nodesPerReplica ) )
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@sftim . Changes seem fine. Small nit as to whether line 135 change is needed.
/lgtm

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I'd use MathML if I had a chance!

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/approve

Note that the values of both `coresPerReplica` and `nodesPerReplica` are
integers.
Expand Down Expand Up @@ -242,22 +226,10 @@ the autoscaler Pod.
* The autoscaler provides a controller interface to support two control
patterns: *linear* and *ladder*.

## Future enhancements

Control patterns, in addition to linear and ladder, that consider custom metrics
are under consideration as a future development.

Scaling of DNS backends based on DNS-specific metrics is under consideration as
a future development. The current implementation, which uses the number of nodes
and cores in cluster, is limited.

Support for custom metrics, similar to that provided by
[Horizontal Pod Autoscaling](/docs/tasks/run-application/horizontal-pod-autoscale/),
is under consideration as a future development.

{{% /capture %}}

{{% capture whatsnext %}}
* Read about [Guaranteed Scheduling For Critical Add-On Pods](/docs/tasks/administer-cluster/guaranteed-scheduling-critical-addon-pods/).
* Learn more about the
[implementation of cluster-proportional-autoscaler](https://github.com/kubernetes-incubator/cluster-proportional-autoscaler).
{{% /capture %}}