# How to Re-deploy CoreDNS Pods Only to the Master Nodes.

## Problem

Re-deploy CoreDNS pods only to the master nodes as part of performance improvement. Process to achieve this by editing Clusteraddon and by using taints.

## Environment

* Platform9 Managed Kubernetes - 5.4.0 and Higher.

## Procedure

To implement this via the taint and toleration method, the steps to be performed is to set `watch` flag to `false` in CoreDNS clusteraddon object and manually edit the CoreDNS deployment to add taints.

{% tabs %}
{% tab title="CoreDNS ClusterAddon" %}

```c
Edit watch flag to false in clusteraddon of CoreDNS:

# kubectl edit clusteraddons -n default 91bc678c-7da5-41d0-be51-c295cd0a6453-coredns
```

{% endtab %}
{% endtabs %}

#### **After editing:**

{% tabs %}
{% tab title="CoreDNS ClusterAddon" %}

```c
# kubectl describe clusteraddons -n default 91bc678c-7da5-41d0-be51-c295cd0a6453-coredns
Name:         91bc678c-7da5-41d0-be51-c295cd0a6453-coredns
Namespace:    default
Labels:       sunpike.pf9.io/cluster=91bc678c-7da5-41d0-be51-c295cd0a6453
              type=coredns
Annotations:  <none>
API Version:  sunpike.platform9.com/v1alpha2
Kind:         ClusterAddon

Spec:
  Cluster ID:  91bc678c-7da5-41d0-be51-c295cd0a6453
  Override:
    Params:
      Name:   dnsMemoryLimit
      Value:  170Mi
      Name:   dnsDomain
      Value:  cluster.local
  Type:       coredns
  Version:    1.8.0
  Watch:      false   < ---------------------
```

{% endtab %}
{% endtabs %}

Add toleration to CoreDNS deployment:

{% tabs %}
{% tab title="CoreDNS Deployment" %}

```c
nodeSelector:                                    
      node-role.kubernetes.io/master: ""            <--------- Add 
      priorityClassName: system-cluster-critical
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      serviceAccount: coredns
      serviceAccountName: coredns
      terminationGracePeriodSeconds: 30
      tolerations:
      - key: CriticalAddonsOnly
        operator: Exists
      - effect: NoSchedule                            <--------- Add
        key: node-role.kubernetes.io/master           <--------- Add
        operator: Equal                               <--------- Add 
        value: "true"                                 <--------- Add
```

{% endtab %}
{% endtabs %}

The CoreDNS pods will be re-deploy to master node/s only:

{% tabs %}
{% tab title="CoreDNS Pods" %}

```c
# k get pods -A -owide | grep core
kube-system            coredns-84fffcdbd6-52p4j                     1/1     Running       0          10s   10.20.73.133     10.128.147.114   <none>           <none>
kube-system            coredns-84fffcdbd6-shng9                     1/1     Running       0          10s   10.20.73.134     10.128.147.114   <none>           <none>
kube-system            coredns-88d66bcc7-rlxqr                      1/1     Terminating   0          35m   10.20.165.196    10.128.147.204   <none>           <none>
```

{% endtab %}
{% endtabs %}

## Additional Information

The changes made will not persists across cluster upgrade. The new version CoreDNS yaml post upgrade wipes out the taints and toleration.


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