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. Currently, two scaling modes are supported: Linear mode and Ladder mode.

Linear Mode

ConfigMap sample 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

ConfigMap sample 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 number 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 larger value of the two is 3, so replica = 3.

Kubernetes objects deployed in a cluster

Limits

• It only supports clusters with Kubernetes version 1.8 and later.
• The workload of the DNS server in the cluster should be deployment/coredns.

Usage

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 policy 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 on the configuration, see the official documentation.
5. Click Done.