script for updating DNS records dynamically via RFC 2136

rfc2136_dynDNS.py

from json import load
from sys import argv
import subprocess
from time import sleep, monotonic


with open(argv[1],"r") as file:
	config=load(file)

def send_nsupdate(ip,domain,keyfile,server,zone,ttl=60):
	cmd=f"""server {server}
zone {zone}
update delete {domain} AAAA
send
update add {domain} {ttl} AAAA {ip[1]}
send
update delete {domain} A
send
update add {domain} {ttl} A {ip[0]}
send
quit"""
	#print(cmd)
	sp = subprocess.run(['nsupdate', '-k', keyfile], input=cmd, text=True)
	if sp.returncode != 0:
		print("ERROR, return code",sp.returncode)
	else:
		print(domain,"OK")
def update_ip(conf,ip):
	for host in config["hosts"]:
		send_nsupdate(ip,host["domain"],host["keyfile"],host["server"],host["zone"],host["ttl"])

def get_ip(conf):
	v4=subprocess.check_output(config["ipv4_cmd"]).decode('utf-8').strip()
	v6=subprocess.check_output(config["ipv6_cmd"]).decode('utf-8').strip()
	return (v4,v6)

prev_ip=(None,None)
last_update_time=0
while True:
	try:
		ip=get_ip(config)
	except subprocess.CalledProcessError:
		sleep(int(config["interval"]))
		continue
	seconds_since_last_update = monotonic() - last_update_time
	if ip != prev_ip or seconds_since_last_update > config['max_interval']:
		print("Updating to",ip)
		update_ip(config,ip)
		prev_ip=ip
		last_update_time=monotonic()
	else:
		print("IP has not changed")
	print()
	sleep(int(config["interval"]))

rfc2136_dynDNS.service

[Unit]
Description=RFC 2136 Dynamic DNS Update Client
Wants=network-online.target
After=network-online.target nss-lookup.target

[Service]
Type=exec
User=dyndns
ExecStart=python3 /opt/rfc2136_updater.py /etc/rfc2136/conf.json
Restart=on-failure

[Install]
WantedBy=multi-user.target

zzzz.config.example.json

{
"interval": 10,
"max_interval": 3600,
"ipv4_cmd": ["bash","/opt/fritzbox_ipv4.sh"],
"ipv6_cmd": ["bash","/opt/interface_ipv6.sh"],

"hosts": [
{
"server": "45.129.95.255",
"keyfile": "/etc/rfc2136/glauca-aaaa.private",
"ttl": "120",
"zone": "example.com",
"domain": "aaaa.example.com"
},
{
"server": "45.129.95.255",
"keyfile": "/etc/rfc2136/glauca-bbbb.private",
"ttl": "120",
"zone": "example.com",
"domain": "bbbb.example.com"
}
]
}

zzzz.ipv4_fritzbox.sh

#!/bin/bash
# 
# Script to fetch IP from fritzbox
#
# Contributed by @Rusk85 in request #45
# Script can be used in the configuration by adding
#
#    use=cmd, cmd=/etc/ddclient/get-ip-from-fritzbox
#
# All credits for this one liner go to the author of this blog:
# http://scytale.name/blog/2010/01/fritzbox-wan-ip
# Disclaimer: It might be necessary to make the script executable

# Set default hostname to connect to the FritzBox
: ${FRITZ_BOX_HOSTNAME:=fritz.box}

curl -s -H 'Content-Type: text/xml; charset="utf-8"' \
  -H 'SOAPAction: urn:schemas-upnp-org:service:WANIPConnection:1#GetExternalIPAddress' \
  -d '<?xml version="1.0" encoding="utf-8"?><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"> <s:Body> <u:GetExternalIPAddress xmlns:u="urn:schemas-upnp-org:service:WANIPConnection:1" /></s:Body></s:Envelope>' \
  "http://$FRITZ_BOX_HOSTNAME:49000/igdupnp/control/WANIPConn1" | \
  grep -Eo '\<[[:digit:]]{1,3}(\.[[:digit:]]{1,3}){3}\>'

zzzz.ipv6_interface.sh

ip -6 addr show scope global | sed -e's/^.*inet6 \([^ ]*\)\/.*$/\1/;t;d' | grep ^2 | grep IPV6_HOST_ID_HERE | head -n 1