Disabling and Understanding DNS Horizontal Autoscaling

The idea is that when a cluster is using nodes that have many cores, `coresPerReplica` dominates. When a cluster is using nodes that have fewer cores, `nodesPerReplica` dominates. There are other supported scaling patterns. For details, see [cluster-proportional-autoscaler](https://github.com/kubernetes-sigs/cluster-proportional-autoscaler). ## Disable DNS horizontal autoscaling There are a few options for tuning DNS horizontal autoscaling. Which option to use depends on different conditions. ### Option 1: Scale down the kube-dns-autoscaler deployment to 0 replicas This option works for all situations. Enter this command: ```shell kubectl scale deployment --replicas=0 kube-dns-autoscaler --namespace=kube-system ``` The output is: deployment.apps/kube-dns-autoscaler scaled Verify that the replica count is zero: ```shell kubectl get rs --namespace=kube-system ``` The output displays 0 in the DESIRED and CURRENT columns: NAME DESIRED CURRENT READY AGE ... kube-dns-autoscaler-6b59789fc8 0 0 0 ... ... ### Option 2: Delete the kube-dns-autoscaler deployment This option works if kube-dns-autoscaler is under your own control, which means no one will re-create it: ```shell kubectl delete deployment kube-dns-autoscaler --namespace=kube-system ``` The output is: deployment.apps "kube-dns-autoscaler" deleted ### Option 3: Delete the kube-dns-autoscaler manifest file from the master node This option works if kube-dns-autoscaler is under control of the (deprecated) [Addon Manager](https://git.k8s.io/kubernetes/cluster/addons/README.md), and you have write access to the master node. Sign in to the master node and delete the corresponding manifest file. The common path for this kube-dns-autoscaler is: /etc/kubernetes/addons/dns-horizontal-autoscaler/dns-horizontal-autoscaler.yaml After the manifest file is deleted, the Addon Manager will delete the kube-dns-autoscaler Deployment.  ## Understanding how DNS horizontal autoscaling works * The cluster-proportional-autoscaler application is deployed separately from the DNS service. * An autoscaler Pod runs a client that polls the Kubernetes API server for the number of nodes and cores in the cluster. * A desired replica count is calculated and applied to the DNS backends based on the current schedulable nodes and cores and the given scaling parameters. * The scaling parameters and data points are provided via a ConfigMap to the autoscaler, and it refreshes its parameters table every poll interval to be up to date with the latest desired scaling parameters. * Changes to the scaling parameters are allowed without rebuilding or restarting the autoscaler Pod. * The autoscaler provides a controller interface to support two control patterns: *linear* and *ladder*. ## {{% heading "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-sigs/cluster-proportional-autoscaler).

This section outlines three options to disable DNS horizontal autoscaling: scaling down the kube-dns-autoscaler deployment to 0 replicas, deleting the kube-dns-autoscaler deployment, or deleting the kube-dns-autoscaler manifest file from the master node (if managed by the Addon Manager). It then explains how DNS horizontal autoscaling works, detailing the cluster-proportional-autoscaler application, polling of the Kubernetes API server, calculation and application of the desired replica count, use of ConfigMap for scaling parameters, and controller interface supporting linear and ladder control patterns. Finally, it suggests further reading on guaranteed scheduling for critical add-on pods and the implementation of cluster-proportional-autoscaler.