DDNS with a Linode domain

ddns.sh

#!/bin/sh

# Linode DDNS Updater script
# By Will Vincent <will@willvincent.com>
#
# Requirements:
#  - A Linode account (obviously)
#  - A domain record already created to update with the script
#  - curl & jq
#
# Usage:
#   Follow api instructions to setup a personal access token
#   and then make queries to find the domain and record ids
#
#   Run with a cron job..  Known to work on openwrt, should
#   also run anywhere linux-ish that has curl and jq commands
#   a basic shell (sh, ash, bash, etc), with an internet
#   connection to the outsie world.


# ------------------------------------------------------
# Configuration
# ------------------------------------------------------
TOKEN=PutYourTokenHere
DOMAIN_ID=PutYourIdHere
RECORD_ID=PutYourRecordIdHere

# Set full path if you want it elsewhere than alongside
# this script file.
LOGFILE=ddns.log

# ------------------------------------------------------

PUBLIC_IP=`curl -s https://ipinfo.io/ip`
CURRENT_IP=`curl -s -H "Authorization: Bearer $TOKEN" https://api.linode.com/v4/domains/$DOMAIN_ID/records/$RECORD_ID | jq -r .target`

payload() {
  cat <<EOF
{
  "target": "$PUBLIC_IP"
}
EOF
}

# Only update if our IP differs from that already in the domain record
if [ "$CURRENT_IP" != "$PUBLIC_IP" ]
then
  if LC_ALL=C awk 'BEGIN{exit(!(ARGV[1] ~ /^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$/))}' "$PUBLIC_IP"
    then
      curl -H "Authorization: Bearer $TOKEN" -H "Content-Type: application/json" -X PUT -d "$(payload)" https://api.linode.com/v4/domains/$DOMAIN_ID/records/$RECORD_ID > /dev/null
      echo "$(date) :: IP Updated from $CURRENT_IP to $PUBLIC_IP" >> $LOGFILE
    else
      echo "$(date) :: Invalid IP! $PUBLIC_IP" >> $LOGFILE
      # Might also want to fire off an email here...
  fi
fi