Autoscaling CoreDNS

Ensure that your cluster is at or above the minimum cluster version.

Amazon EKS upgrades clusters between platform versions of the same Kubernetes version automatically, and you can’t start this process yourself. Instead, you can upgrade your cluster to the next Kubernetes version, and the cluster will be upgraded to that K8s version and the latest platform version. For example, if you upgrade from 1.25 to 1.26, the cluster will upgrade to 1.26.15 eks.18.

New Kubernetes versions sometimes introduce significant changes. Therefore, we recommend that you test the behavior of your applications by using a separate cluster of the new Kubernetes version before you update your production clusters.

To upgrade a cluster to a new Kubernetes version, follow the procedure in Updating an Amazon EKS cluster Kubernetes version.

Ensure that you have the EKS Add-on for CoreDNS, not the self-managed CoreDNS Deployment.

Depending on the tool that you created your cluster with, you might not currently have the Amazon EKS add-on type installed on your cluster. To see which type of the add-on is installed on your cluster, you can run the following command. Replace my-cluster with the name of your cluster.

aws eks describe-addon --cluster-name my-cluster --addon-name coredns --query addon.addonVersion --output text
                        

If a version number is returned, you have the Amazon EKS type of the add-on installed on your cluster and you can continue with the next step. If an error is returned, you don't have the Amazon EKS type of the add-on installed on your cluster. Complete the remaining steps of the procedure Creating the Amazon EKS add-on to replace the self-managed version with the Amazon EKS add-on.

Ensure that your EKS Add-on for CoreDNS is at a version the same or higher than the minimum EKS Add-on version.

See which version of the add-on is installed on your cluster. You can check in the AWS Management Console or run the following command:

kubectl describe deployment coredns --namespace kube-system | grep coredns: | cut -d : -f 3
                        

An example output is as follows.

v1.10.1-eksbuild.11

Compare this version with the minimum EKS Add-on version in the previous section. If needed, upgrade the EKS Add-on to a higher version by following the procedure Updating the Amazon EKS add-on.

Add the autoscaling configuration to the Optional configuration settings of the EKS Add-on.

1. Open the Amazon EKS console at https://console.aws.amazon.com/eks/home#/clusters.

2. In the left navigation pane, select Clusters, and then select the name of the cluster that you want to configure the add-on for.

3. Choose the Add-ons tab.

4. Select the box in the top right of the CoreDNS add-on box and then choose Edit.

5. On the Configure CoreDNS page:

   1. Select the Version that you'd like to use. We recommend that you keep the same version as the previous step, and update the version and configuration in separate actions.

   2. Expand the Optional configuration settings.

   3. Enter the JSON key "autoscaling": and value of a nested JSON object with a key "enabled": and value true in Configuration values. The resulting text must be a valid JSON object. If this key and value are the only data in the text box, surround the key and value with curly braces {}. The following example shows autoscaling is enabled:

      {
        "autoScaling": {
          "enabled": true
        }
      }

   4. (Optional) You can provide minimum and maximum values that autoscaling can scale the number of CoreDNS pods to.

      The following example shows autoscaling is enabled and all of the optional keys have values. We recommend that the minimum number of CoreDNS pods is always greater than 2 to provide resilience for the DNS service in the cluster.

      {
        "autoScaling": {
          "enabled": true,
          "minReplicas": 2,
          "maxReplicas": 10
        }
      }

6. To apply the new configuration by replacing the CoreDNS pods, choose Save changes.

   Amazon EKS applies changes to the EKS Add-ons by using a rollout of the Kubernetes Deployment for CoreDNS. You can track the status of the rollout in the Update history of the add-on in the AWS Management Console and with kubectl rollout status deployment/coredns --namespace kube-system.

   kubectl rollout has the following commands:

   $ kubectl rollout
                               
   history  -- View rollout history
   pause    -- Mark the provided resource as paused
   restart  -- Restart a resource
   resume   -- Resume a paused resource
   status   -- Show the status of the rollout
   undo     -- Undo a previous rollout
                               

   If the rollout takes too long, Amazon EKS will undo the rollout, and a message with the type of Addon Update and a status of Failed will be added to the Update history of the add-on. To investigate any issues, start from the history of the rollout, and run kubectl logs on a CoreDNS pod to see the logs of CoreDNS.

If the new entry in the Update history has a status of Successful, then the rollout has completed and the add-on is using the new configuration in all of the CoreDNS pods. As you change the number of nodes and CPU cores of nodes in the cluster, Amazon EKS scales the number of replicas of the CoreDNS deployment.

Ensure that your cluster is at or above the minimum cluster version.

Amazon EKS upgrades clusters between platform versions of the same Kubernetes version automatically, and you can’t start this process yourself. Instead, you can upgrade your cluster to the next Kubernetes version, and the cluster will be upgraded to that K8s version and the latest platform version. For example, if you upgrade from 1.25 to 1.26, the cluster will upgrade to 1.26.15 eks.18.

New Kubernetes versions sometimes introduce significant changes. Therefore, we recommend that you test the behavior of your applications by using a separate cluster of the new Kubernetes version before you update your production clusters.

To upgrade a cluster to a new Kubernetes version, follow the procedure in Updating an Amazon EKS cluster Kubernetes version.

Ensure that you have the EKS Add-on for CoreDNS, not the self-managed CoreDNS Deployment.

Depending on the tool that you created your cluster with, you might not currently have the Amazon EKS add-on type installed on your cluster. To see which type of the add-on is installed on your cluster, you can run the following command. Replace my-cluster with the name of your cluster.

aws eks describe-addon --cluster-name my-cluster --addon-name coredns --query addon.addonVersion --output text
                        

If a version number is returned, you have the Amazon EKS type of the add-on installed on your cluster. If an error is returned, you don't have the Amazon EKS type of the add-on installed on your cluster. Complete the remaining steps of the procedure Creating the Amazon EKS add-on to replace the self-managed version with the Amazon EKS add-on.

Ensure that your EKS Add-on for CoreDNS is at a version the same or higher than the minimum EKS Add-on version.

See which version of the add-on is installed on your cluster. You can check in the AWS Management Console or run the following command:

kubectl describe deployment coredns --namespace kube-system | grep coredns: | cut -d : -f 3
                        

An example output is as follows.

v1.10.1-eksbuild.11

Compare this version with the minimum EKS Add-on version in the previous section. If needed, upgrade the EKS Add-on to a higher version by following the procedure Updating the Amazon EKS add-on.

Add the autoscaling configuration to the Optional configuration settings of the EKS Add-on.

Run the following AWS CLI command. Replace my-cluster with the name of your cluster and the IAM role ARN with the role that you are using.

aws eks update-addon --cluster-name my-cluster --addon-name coredns \
    --resolve-conflicts PRESERVE --configuration-values '{"autoScaling":{"enabled":true}}'
                        

Amazon EKS applies changes to the EKS Add-ons by using a rollout of the Kubernetes Deployment for CoreDNS. You can track the status of the rollout in the Update history of the add-on in the AWS Management Console and with kubectl rollout status deployment/coredns --namespace kube-system.

kubectl rollout has the following commands:

kubectl rollout
                            
history  -- View rollout history
pause    -- Mark the provided resource as paused
restart  -- Restart a resource
resume   -- Resume a paused resource
status   -- Show the status of the rollout
undo     -- Undo a previous rollout
                            

If the rollout takes too long, Amazon EKS will undo the rollout, and a message with the type of Addon Update and a status of Failed will be added to the Update history of the add-on. To investigate any issues, start from the history of the rollout, and run kubectl logs on a CoreDNS pod to see the logs of CoreDNS.

(Optional) You can provide minimum and maximum values that autoscaling can scale the number of CoreDNS pods to.

The following example shows autoscaling is enabled and all of the optional keys have values. We recommend that the minimum number of CoreDNS pods is always greater than 2 to provide resilience for the DNS service in the cluster.

aws eks update-addon --cluster-name my-cluster --addon-name coredns \
    --resolve-conflicts PRESERVE --configuration-values '{"autoScaling":{"enabled":true,"minReplicas":2,"maxReplicas":10}}'
                        

Check the status of the update to the add-on by running the following command:

aws eks describe-addon --cluster-name my-cluster --addon-name coredns \
                    

If you see this line: "status": "ACTIVE", then the rollout has completed and the add-on is using the new configuration in all of the CoreDNS pods. As you change the number of nodes and CPU cores of nodes in the cluster, Amazon EKS scales the number of replicas of the CoreDNS deployment.