How to check the default CoreDNS configmap of a Rancher Kubernetes Engine (RKE) Kubernetes version

This document (000020036) is provided subject to the disclaimer at the end of this document.



You might have modified the default configmap for CoreDNS using Rancher Kubernetes Engine's (RKE) cluster configuration YAML (cluster.yml). In this case, you may want to know the default configmap prior to upgrading Kubernetes. This verification step will help you to add all of the default/mandatory parameters to the modified configmap in RKE's cluster.yml, upon upgrade.


  • python2


Download the kontainer-metadata according to the Rancher version you are running.

Rancher 2.4.x:

curl -O

Rancher v2.5.x:

curl -O

Get the available template list:

python2 -c "import sys, json; d=json.load(sys.stdin)['K8sVersionedTemplates']['coreDNS']; print json.dumps(d,indent=4)" <data.json


    ">=1.8.0-rancher0 <1.16.0-alpha": "coredns-v1.8",
    ">=1.17.0-alpha": "coredns-v1.17",
    ">=1.16.0-alpha <1.17.0-alpha": "coredns-v1.16"

Translation of one of the entry from the list is as follows:

">=1.8.0-rancher0 <1.16.0-alpha": "coredns-v1.8",

If Kubenetes version is greater than or equal to 1.8.0-rancher0 and less than 1.16.0-alpha ,then the CoreDNS key we have to use in next step is coredns-v1.8

python2 -c "import sys, json; print json.load(sys.stdin)['K8sVersionedTemplates']['templateKeys']['coredns-v1.8']" <data.json

The configmap will be printed on the screen along with other YAML template specs associated with CoreDNS.

Sample output:

apiVersion: v1
kind: ConfigMap
  name: coredns
  namespace: kube-system
  labels: EnsureExists
  Corefile: |
    .:53 {
        kubernetes {{.ClusterDomain}} {{ if .ReverseCIDRs }}{{ .ReverseCIDRs }}{{ else }}{{ "" }}{{ end }} {
          pods insecure
          ttl 30
        prometheus :9153
    {{- if .UpstreamNameservers }}
        forward . {{range $i, $v := .UpstreamNameservers}}{{if $i}} {{end}}{{.}}{{end}}
    {{- else }}
        forward . "/etc/resolv.conf"
    {{- end }}
        cache 30


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  • Document ID:000020036
  • Creation Date: 06-May-2021
  • Modified Date:06-May-2021
    • SUSE Rancher

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