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.

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.

Edit watch flag to false in clusteraddon of CoreDNS:

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

After editing:

# 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 < ---------------------

Add toleration to CoreDNS deployment:

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

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

# 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>

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

Problem

Environment

Procedure

After editing:

Additional Information