DIY dDNS service script using Hetzner's DNS API

update-ddns.rb

#!/usr/bin/env ruby
# on OpenRC systems, place into e.g. /etc/periodic/15min
# (or create /etc/periodic/1min and add line to root's crontab)
# on systemd systems, install it as a timer

# create/find these in Hetzner's DNS admin interface at https://dns.hetzner.com/
API_TOKEN_NAME="..."
API_TOKEN="..."

ZONES=["...", "..."] # TLD; must be registered at https://robot.hetzner.com/domain
RECORDS=["...", "..."] # list of subdomains, also specified there

# will be a bit faster if specified
# ZONE_ID="..."
# RECORD_ID="..."

require 'json'
require 'socket'

ZONES.each do |zone|
  @zone_id = ZONE_ID ? ZONE_ID : (
    json = JSON.parse `curl -s "https://dns.hetzner.com/api/v1/zones" -H "Auth-API-Token: #{API_TOKEN}"`
    zones_json = json.delete('zones')
    zones_json.find{|x| x['name']==zone}['id']
  )

  json = JSON.parse `curl -s "https://dns.hetzner.com/api/v1/records?zone_id=#{@zone_id}" -H "Auth-API-Token: #{API_TOKEN}"`
  records_json = json.delete('records')

  RECORDS.each do |record|
    record_json = records_json.find{|x| x['name']==record}
    @record_id ||= record_json['id']
    current_record_ip = record_json['value']
    current_wan_ip = Socket.getifaddrs
                       .map{|iface| [iface.name, iface.addr.ip_address] if iface.addr.ipv4? if iface.addr}
                       .compact
                       .find{|x| x[0]=='ppp0'}[1]

    next if current_record_ip == current_wan_ip

    system %Q(
      curl -X "PUT" "https://dns.hetzner.com/api/v1/records/#{@record_id}" \\
           -H "Content-Type: application/json" \\
           -H "Auth-API-Token: #{API_TOKEN}" \\
           -d $'{
        "value": "#{current_wan_ip}",
        "ttl": 60,
        "type": "A",
        "name": "#{record}",
        "zone_id": "#{@zone_id}"
      }'
    )
  end
end