current unmodified configmap for coredns

gathering the coredns configmap on a fresh/unmodified setup:

demo@Ubuntu-2204-jammy-amd64-base:~/wire-server-deploy$ d kubectl get configmap coredns -n kube-system --output yaml
apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health {
            lameduck 5s
        }
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
          pods insecure
          fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf {
          prefer_udp
          max_concurrent 1000
        }
        cache 30

        loop
        reload
        loadbalance
    }
kind: ConfigMap
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"v1","data":{"Corefile":".:53 {\n    errors\n    health {\n        lameduck 5s\n    }\n    ready\n    kubernetes cluster.local in-addr.arpa ip6.arpa {\n      pods insecure\n      fallthrough in-addr.arpa ip6.arpa\n    }\n    prometheus :9153\n    forward . /etc/resolv.conf {\n      prefer_udp\n      max_concurrent 1000\n    }\n    cache 30\n\n    loop\n    reload\n    loadbalance\n}\n"},"kind":"ConfigMap","metadata":{"annotations":{},"labels":{"addonmanager.kubernetes.io/mode":"EnsureExists"},"name":"coredns","namespace":"kube-system"}}
  creationTimestamp: "2023-10-02T23:51:43Z"
  labels:
    addonmanager.kubernetes.io/mode: EnsureExists
  name: coredns
  namespace: kube-system
  resourceVersion: "994"
  uid: e9bfcb9b-2493-4614-8fc0-c861c4bac997

current unmodified configmap for nodelocaldns

gathering the nodelocaldns configmap on a fresh/unmodified setup:

demo@Ubuntu-2204-jammy-amd64-base:~/wire-server-deploy$ d kubectl get configmap nodelocaldns -n kube-system -o=jsonpath='{.data.Corefile}'
cluster.local:53 {
    errors
    cache {
        success 9984 30
        denial 9984 5
    }
    reload
    loop
    bind 10.233.0.10
    forward . 10.233.0.3 {
        force_tcp
    }
    prometheus :9253
    health 10.233.0.10:9254
}
in-addr.arpa:53 {
    errors
    cache 30
    reload
    loop
    bind 10.233.0.10
    forward . 10.233.0.3 {
        force_tcp
    }
    prometheus :9253
}
ip6.arpa:53 {
    errors
    cache 30
    reload
    loop
    bind 10.233.0.10
    forward . 10.233.0.3 {
        force_tcp
    }
    prometheus :9253
}
.:53 {
    errors
    cache 30
    reload
    loop
    bind 10.233.0.10
    forward . /etc/resolv.conf
    prometheus :9253
}

Instructions to manually reverse the effects of the script.

## Editing coredns config.

1. Get config into a file.

d kubectl get configmap coredns -n kube-system --output yaml > coredns_config.yaml

2. Modify the file.

Replacing:

        forward . 127.0.0.53:9999 {
            max_fails 0
        }
        
With:

        forward . /etc/resolv.conf {
          prefer_udp
          max_concurrent 1000
        }

3. Apply the file.

d kubectl apply -f coredns_config.yaml

## Editing nodelocaldns config.

1. Get config into a file.

d kubectl get configmap nodelocaldns -n kube-system --output yaml > nodelocaldns_config.yaml

2. Modify the file:

Add `forward . /etc/resolv.conf` where it is missing between `bind 10.233.0.10` and `prometheus :9253`, around line 45.

So that:

        bind 10.233.0.10
        prometheus :9253

Becomes:

        bind 10.233.0.10
        forward . /etc/resolv.conf
        prometheus :9253

3. Apply the file.

d kubectl apply -f nodelocaldns_config.yaml

script analysis and instructions to reverse it.

## Analysis of the script:

The nodelocaldns part of the script:

1. Obtains the content of the configMap for nodelocaldns
2. Deletes the `forward . /etc/resolv.conf` line (line 45) from that configMap
3. Replaces the configmap with the configmap that is missing that line.

The modifier line is:
MODIFIED_TEXT=$(echo "$CURRENT_COREFILE" | sed '/forward \. \/etc\/resolv\.conf/d')

The coredns part of the script:

1. Obtains the content of the configMap for nodelocaldns
2. Finds any line that starts with "forward", and deletes it as well as the next 3 lines:

        forward . /etc/resolv.conf {
          prefer_udp
          max_concurrent 1000
        }
        
3. Finds any line that starts with "cache", and replaces it with:

        forward . 127.0.0.53:9999 {
            max_fails 0
        }
        cache
        
4. Replaces the configmap with the configmap that is thus modified.

This line is essentially equivalent with replacing:

        forward . /etc/resolv.conf {
          prefer_udp
          max_concurrent 1000
        }
        
with:

        forward . 127.0.0.53:9999 {
            max_fails 0
        }

The modifier line is:
sed -i coredns_config.yaml -e '/^[ ]*forward.*/{N;N;N;d;}' -e "s/^\([ ]*\)cache/\1forward . 127.0.0.53:9999 {\n\1  max_fails 0\n\1}\n\1cache/"

## Instructions to reverse the script.

0. Presuming the script was run, and we want to revert its effects.
1. Gather the nodelocaldns configmap with: `kubectl get configmap nodelocaldns -n kube-system -o=jsonpath='{.data.Corefile}'`
2. Save the returned data to a `nodelocaldns_config.yaml` file and edit it by adding `forward . /etc/resolv.conf` where it is missing between `bind 10.233.0.10` and `prometheus :9253`, around line 45.
4. Apply this change using the command `kubectl apply -f nodelocaldns_config.yaml`
5. Gather the coredns configmap with: `kubectl get configmap coredns -n kube-system --output yaml`
6. Save the data to a `coredns_config.yaml` file and modify the returned data, replacing:

        forward . 127.0.0.53:9999 {
            max_fails 0
        }
        
with:

        forward . /etc/resolv.conf {
          prefer_udp
          max_concurrent 1000
        }
        
7. Commit the modified data using the command `kubectl apply -f coredns_config.yaml`

Script to automatically revert the effects of the script:

#!/bin/bash
# Script to edit coredns and nodelocaldns configs in a Kubernetes cluster

# Load the environment.
d='sudo docker run -it --network=host -v nonexistent:/ssh-agent -e SSH_AUTH_SOCK=/ssh-agent -v /home/demo/.ssh:/root/.ssh -v /home/demo/wire-server-deploy:/wire-server-deploy quay.io/wire/wire-server-deploy:i045hf4fc3ffszb5s7kir3dg0jk2lrcb'
#!/bin/bash

# Make sure the script fails on any error
set -e

# Editing coredns config
echo "Editing coredns config..."

# Get the coredns config into a file
$d kubectl get configmap coredns -n kube-system --output yaml > coredns_config.yaml

# Function to replace text in a file
replace_text() {
  local search_for="$1"
  local replace_with="$2"
  local file="$3"

  # Use sed to replace text
  sed -i "s/${search_for}/${replace_with}/g" "$file"
}

# File to be edited
file_to_edit="coredns_config.yaml" 

# Text to be replaced and its replacement
# We use [[:space:]] to match any number of white-space characters
# Escape special characters in the search text
search1="forward . 127.0.0.53:9999"
replace1="forward . \/etc\/resolv.conf"

search2="max_fails 0"
replace2="prefer_udp\n          max_concurrent 1000"

# Perform the replacements
replace_text "$search1" "$replace1" "$file_to_edit"
replace_text "$search2" "$replace2" "$file_to_edit"

# Confirmation message
echo "Text successfully replaced in $file_to_edit."

# Apply the changes
$d kubectl apply -f coredns_config.yaml

echo "Finished editing coredns config."

# Editing nodelocaldns config
echo "Editing nodelocaldns config..."

# Function to replace text in a file
replace_text_in_file() {
  # Parameters: Old text, New text, File name
  awk -v old="$1" -v new="$2" '
    {
      gsub(old, new)
    }
    {
      print
    }
  ' $3 > tmpfile && mv tmpfile $3
}

# Make sure the script fails on any error
set -e

# Text to be replaced
old_text="        bind 10.233.0.10\n        prometheus :9253"
# Text to replace with
new_text="        bind 10.233.0.10\n        forward . /etc/resolv.conf\n        prometheus :9253"

# Get the nodelocaldns config into a file
$d kubectl get configmap nodelocaldns -n kube-system --output yaml > nodelocaldns_config.yaml

# Use replace_text_in_file function to replace the text
replace_text_in_file "$old_text" "$new_text" "nodelocaldns_config.yaml"

# Apply the changes
$d kubectl apply -f nodelocaldns_config.yaml

echo "Finished editing nodelocaldns config."