Cloudflare Dynamic DNS Script in Bash

cloudflare-ddns.service

[Unit]
Description=Cloudflare DDNS Service

[Service]
Type=simple
ExecStart=/full/path/to/cloudflare-ddns.sh
TimeoutStopSec=20

cloudflare-ddns.sh

#!/bin/bash

# A bash script to manage a DNS records in Cloudflare to create a simple
# Dynamic DNS service. This script will first try to get the external gateway
# IP of this machine and then update A records in cloudflare to point a set of
# hostnames to this external IP. This script expects the records to already be
# present in the zone.

# Setup:
# - Login to your cloudflare account and click on the Zone/Domain to update.
#   In the overview page, look for the Zone ID and update the zone_id below
# - On the same page, look for 'Get you API Token' link and click on it.
#   Click on 'API Tokens' tab and create a new token. Choose the 'Edit Zone DNS'
#   template. Check the Permissions section has Zone -> DNS -> Edit in the three
#   dropdowns. In Zone Resources, the first two dropdowns should be Include ->
#   Specific Zone. In the third dropdown choose the zone to update.
#   Click on 'Continue to summary' and verify everything looks good and click on
#   'Create Token'. The next page will display the API Token. Copy it and update
#   cf_bearer_token line below.
# - domain: The domain name of the zone
# - hosts: The hostnames without the domain that need to be updated.

###############################################################################
## SCRIPT VARIABLES
# Cloudflare API/Bearer Token
cf_bearer_token=

# Cloudflare zone for the hostname
zone_id=
# This should match the zone_id
domain=example.com

# The hostnames to update
hosts=(www mail home)

# Set this to true to enable cloudflare DNS proxy (orange cloud) or
# false to disable (grey cloud)
proxy="true"
##############################################################################

verbose=''
force=''

while getopts ":fv" opt; do
  case ${opt} in
    f ) # force update
      force='y'
      ;;
    v ) # verbose mode
      verbose='-v'
      ;;
    \? )
      ;;
  esac
done

# No of records to update
num_hosts=${#hosts[@]}

if (( $num_hosts < 1 )); then
  echo "No hosts to update. Check the script variable 'hosts'"
  exit 0
fi

dns_record_id="null"
function query_dns_record_id {
  if [[ -z "$1" ]]; then
    return 0
  fi
  hostname=${1}.${domain}
  dns_record_id=$(curl ${verbose} -s "https://api.cloudflare.com/client/v4/zones/${zone_id}/dns_records?type=A&name=${hostname}" \
    -H "Authorization: Bearer $cf_bearer_token" \
    -H "Content-Type: application/json" | jq -r '.result[0].id')
}


# Query the external IP using the AWS CheckIP Service
ext_ip=$(curl -s https://checkip.amazonaws.com)

# Get the first DNS Record ID from cloudflare API
query_dns_record_id ${hosts[0]}

if [[ "$dns_record_id" == "null" ]]; then
  cat <<-ENDMSG
** Unable to extract DNS record-id from Cloudflare APIs. Check the script variables
** or re-run with -v to check the Cloudflare API Call.
ENDMSG
  exit 1
fi

current_ip=$(curl ${verbose} -s "https://api.cloudflare.com/client/v4/zones/${zone_id}/dns_records/${dns_record_id}" \
  -H "Authorization: Bearer $cf_bearer_token" \
  -H "Content-Type: application/json" | jq -r '.result.content')

if [[ "$force" == "y" || "$ext_ip" != "$current_ip" ]]; then
  if [[ "$force" == "y" ]]; then
    echo "Force mode: Updating Cloudflare records"
  else
    echo "External IP [${ext_ip}] is different from IP in cloudflare [${current_ip}]."
    echo "Updating Cloudflare records."
  fi

  # Loop over every host in list $hosts
  for (( i=0; i < ${num_hosts}; i++ )); do
    # we have already queried the dns record-id for the first entry. Skip it.
    if [[ $i -gt 0 ]]; then
      query_dns_record_id ${hosts[$i]}
      if [[ "$dns_record_id" == "null" ]]; then
        echo "Unable to query record-id for ${hosts[$i]}.${domain}. Skipping..."
        continue
      fi
    fi

    # Update the record with the new ip.
    curl -s -X PUT "https://api.cloudflare.com/client/v4/zones/${zone_id}/dns_records/${dns_record_id}" \
      -H "Authorization: Bearer $cf_bearer_token" \
      -H "Content-Type: application/json" \
      --data "{\"type\":\"A\",\"name\":\"${hostname}\",\"content\":\"${ext_ip}\",\"ttl\":1,\"proxied\":${proxy}}" | jq
    echo "Updated Record for ${hostname}"
  done

else
  echo "No change in external IP and cloudflare IP."
fi

cloudflare-ddns.timer

[Unit]
Description=Run Cloudflare DDNS service hourly

[Timer]
OnCalendar=hourly
Persistent=true

[Install]
WantedBy=timers.target