CODEWITHSUNDEEP
kubernetesdnsconfigmapcoredns
Dave
Dave

Reputation: 1255

Is there a way to programmatically update kubernetes core-dns configmap?

I want to be able to add dns record entries to kubernetes core-dns config map. I already know how to do this manually with this

kubectl -n kube-system edit cm coredns

Then add entries under NodeHosts

Is there a supported way to do this? or am I left to my own devices of parsing json and yaml output and replacing config map files with code?

Upvotes: -3

Views: 66

Answers (2)

Dave
Dave

Reputation: 1255

I gave in and just created a python script that does the work for me:

#!/usr/bin/env python3

import subprocess
import json
import os

# Define the entries to add
entries = [
    "127.1.1.11 test1.example.com",
    "127.1.1.12 test2.example.com"
]

namespace = "kube-system"
configmap = "coredns"

def run_command(command):
    result = subprocess.run(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True, check=True)
    return result.stdout.decode('utf-8')

coredns_config_json = run_command(f"kubectl get cm {configmap} -n {namespace} -o json")
coredns_config = json.loads(coredns_config_json)

nodehosts = coredns_config['data'].get('NodeHosts', '')

for entry in entries:
    if entry not in nodehosts:
        nodehosts += f"\n{entry}"

coredns_config['data']['NodeHosts'] = nodehosts
updated_config_json = json.dumps(coredns_config, indent=4)
with open('updated_coredns.json', 'w') as f:
    f.write(updated_config_json)

apply_command = "kubectl apply -f updated_coredns.json"
run_command(apply_command)

os.remove('updated_coredns.json')

print("CoreDNS ConfigMap updated successfully.")

Upvotes: 1

ha36d
ha36d

Reputation: 1127

Technically No, but here are some workarounds:

  • Use custom coredns

The entries can be added via coredns-custom config map, like:

# coredns-custom.yaml

custom.server=example.local:53 {
       hosts {
         192.168.1.101 app1.local
         192.168.1.102 app2.local
         fallthrough
       }
     }

and then

   kubectl -n kube-system create configmap coredns-custom \                                                                                                                     
     --from-file=coredns-custom.yaml -o yaml --dry-run=client | kubectl apply -f -
  • Use kustomize

Create a kustomization.yaml file:

   apiVersion: v1
   kind: ConfigMap
   metadata:
      name: coredns
      namespace: kube-system
   data:
     NodeHosts: |
       192.168.1.100 app.local

and then apply it.

  • Bash Script for Automation

If you frequently update CoreDNS with new hosts, you can automate it with a script:

#!/bin/bash
NEW_ENTRY="192.168.1.101 newapp.local"
kubectl get cm coredns -n kube-system -o yaml | \
  yq e '.data.NodeHosts += "\n'"$NEW_ENTRY"'"' - | \
  kubectl apply -f -
kubectl rollout restart deployment coredns -n kube-system

Upvotes: 0

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