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    DNSAutoscaler

    Last updated: 2024-02-01 10:17:07
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      Overview

      Add-on Description

      DNSAutoscaler is an add-on for DNS horizontal auto scaling. It obtains the number of nodes and cores of a cluster through a Deployment and then automatically scales the number of DNS replicas according to preset scaling policies. Two scaling modes are supported: Linear mode and Ladder mode.

      Linear Mode

      Sample ConfigMap configuration is as follows:
      data:
        linear: |-
          {
            "coresPerReplica": 2,
            "nodesPerReplica": 1,
            "min": 1,
            "max": 100,
            "preventSinglePointFailure": true
          }
      Formula for calculating the number of target replicas: replicas = max(ceil(cores × 1/coresPerReplica) , ceil(nodes × 1/nodesPerReplica))
      replicas = min(replicas, max)
      replicas = max(replicas, min)

      Ladder Mode

      Sample ConfigMap configuration is as follows:
      data:
        ladder: |-
          {
            "coresToReplicas":
            [
              [ 1, 1 ],
              [ 64, 3 ],
              [ 512, 5 ],
              [ 1024, 7 ],
              [ 2048, 10 ],
              [ 4096, 15 ]
            ],
            "nodesToReplicas":
            [
              [ 1, 1 ],
              [ 2, 2 ]
            ]
          }
      Calculating the quantity of target replicas: Assume that the above configuration is applied in a cluster with 100 nodes and 400 cores, then: nodesToReplicas = 2 (100>2), coresToReplicas = 3 (64<400<512), the greater value of the two is 3, so replica = 3.

      Kubernetes objects deployed in a cluster

      Kubernetes Object Name
      Requirement
      Requested Resource
      Namespace
      tke-dns-autoscaler
      Deployment
      20 M CPU and 10 Mi memory per node
      kube-system
      dns-autoscaler
      ConfigMap
      -
      kube-system
      tke-dns-autoscale
      ServiceAccount
      -
      kube-system
      tke-dns-autoscaler
      ClusterRole
      -
      kube-system
      tke-dns-autoscaler
      ClusterRoleBinding
      -
      kube-system

      Limits

      The add-on supports only clusters with Kubernetes version 1.8 and later.
      The workload of the DNS server in the cluster should be Deployment or CoreDNS.

      Notes

      During CoreDNS horizontal scaling, some CoreDNS replicas may be unavailable for a period of time. We recommend that you optimize related configurations to maximize the DNS service availability. For more information, see Configuring Smooth Upgrade.

      Component Permission Description

      Permission Description

      The permission of this component is the minimal dependency required for the current feature to operate.

      Permission Scenarios

      Feature
      Involved Object
      Involved Operation Permission
      Monitoring changes in node resources within the cluster
      node
      list/watch
      
      Modifying the number of coredns replicas deployed by the deployment
      replicationcontrollers/scale, deployments/scale, and replicasets/scale
      get/update
      
      Retrieving parameter configurations from the configmap. In the absence of configured parameters, a configmap with default parameters will be created.
      configmap
      get/create

      Permission Definition

      kind: ClusterRole
      apiVersion: rbac.authorization.k8s.io/v1
      metadata:
        name: tke-dns-autoscaler
      rules:
        - apiGroups:
            - ""
          resources:
            - nodes
          verbs:
            - list
            - watch
        - apiGroups:
            - ""
          resources:
            - replicationcontrollers/scale
          verbs:
            - get
            - update
        - apiGroups:
            - extensions
            - apps
          resources:
            - deployments/scale
            - replicasets/scale
          verbs:
            - get
            - update
        - apiGroups:
            - ""
          resources:
            - configmaps
          verbs:
            - get
            - create

      How to Use

      1. Log in to the TKE console and select Cluster in the left sidebar.
      2. On the Cluster management page, click the ID of the target cluster to go to the cluster details page.
      3. In the left sidebar, click Add-on management to go to the Add-on list page.
      4. On the Add-on list page, click Create. On the Create add-on page, select DNSAutoscaler. The default scaling configuration of this add-on is as follows:
      data:
        ladder: |-
          {
            "coresToReplicas": 
            [
              [ 1, 1 ],
              [ 128, 3 ],
              [ 512, 4 ]
            ],
            "nodesToReplicas": 
            [
              [ 1, 1 ],
              [ 2, 2 ]
            ]
          }
      After the add-on is created successfully, you can modify its configuration by modifying configmap/tke-dns-autoscaler under the kube-system namespace. For more information about the configuration, see the official documentation.
      5. Click Done.
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