dns-update/main.sh

#!/usr/bin/env bash

run_directory=$(dirname $(readlink -f "$0"))
source "$run_directory/variables.conf"

KEY="$run_directory/dns.key"
TTL=604800

FQDN=$(hostname)
MYIP=$(ip route get 8.8.8.8 | grep -oP 'src \K[^ ]+')
MYNUMBER=$(echo $MYIP | cut -d '.' -f 4) # last byte of IP
#MYIP=$(dig +short myip.opendns.com @resolver1.opendns.com)

# if $MYIP is not a valid IP, exit
if [[ ! "$MYIP" =~ ^([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$ ]]; then
  echo "Invalid IP, aborting"
  exit 1
fi

# fetch current record with dig, and choose what to do
# TODO we should probably improve this choice: current implementation prevents hosts that do not have a record yet to register themselves; We'd need to differentiate cases:
# * correct ip, not the same -> OK, need to update
# * correct ip, the same -> OK, nothing to do
# * no result, name server was reachable -> OK, need to register
# * no result, name server was not reachable -> NOK, abort
# * result which is not a correct ip -> NOK, abort
current_ip_record=$(dig $FQDN +short)
if [[ "$current_ip_record" =~ ^([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$ ]]; then
  if [[ ! "$MYIP" = "$current_ip_record" ]]; then
    echo "Updating record"
  else
    echo "Record is already up to date, exiting."
    exit 0
  fi
else
  echo "Server unreachable or no record for $FQDN, exiting."
  exit 0
fi

nsupdate -k $KEY -v << EOF
server $NS
zone $MAINZONE
update delete $FQDN. A
update add $FQDN. $TTL A $MYIP
send
EOF

nsupdate -k $KEY -v << EOF
server $NS
zone $REVERSEZONE
update delete $MYNUMBER.$REVERSEZONE PTR
update add $MYNUMBER.$REVERSEZONE $TTL PTR $FQDN.
send
EOF

exit 0