OpenWRT DDNS with Linode API v4

Here's how I was able to use OpenWRT's native DDNS system with Linode API v4. It works well for me and might work well for others.

/usr/lib/ddns/update_linode_com_v4.sh

# Script for sending user defined updates using the Linode v4 API
# 2015 Artem Yakimenko <code at temik dot me>
# 2021 George Giannou <giannoug at gmail dot com>
# 2024 bluonek  <https://forum.openwrt.org>

# Options passed from /etc/config/ddns:
# domain - Linode domain id (e.g. 1325552)
# password - Linode personal access token (API key)
# param_opt - Linode API record ID of the A/AAAA record (e.g. 21694203)

# Use the following command to find your Linode API domain ID (replace TOKEN with your own):
# curl -X GET -H 'Content-Type: application/json' \
#     -H "Authorization: Bearer TOKEN" \
#     "https://api.linode.com/v4/domains"

# Then use the following command to find your Linode API resource ID (replace TOKEN with your own, and DOMAIN with the domain ID from the previous command):
# curl -X GET -H 'Content-Type: application/json' \
#     -H "Authorization: Bearer TOKEN" \
#     "https://api.linode.com/v4/domains/DOMAIN/records"

. /usr/share/libubox/jshn.sh

[ -z "$domain" ] && write_log 14 "Service section not configured correctly! Missing domain name as 'Domain'"
[ -z "$password" ] && write_log 14 "Service section not configured correctly! Missing personal access token as 'Password'"
[ -z "$param_opt" ] && write_log 14 "Service section not configured correctly! Missing API domain resource ID as 'Optional Parameter'"

# Construct JSON payload
json_init
json_add_string target "$__IP"

__STATUS=$(curl -Ss -X PUT "https://api.linode.com/v4/domains/${domain}/records/${param_opt}" \
    -H "Authorization: Bearer ${password}" \
    -H "Content-Type: application/json" \
    -d "$(json_dump)" \
    -w "%{http_code}\n" -o $DATFILE 2>$ERRFILE)

if [ $? -ne 0 ]; then
    write_log 14 "Curl failed: $(cat $ERRFILE)"
    return 1
elif [ -z $__STATUS ] || [ $__STATUS != 200 ]; then
    write_log 14 "Curl failed: $__STATUS \nlinode.com answered: $(cat $DATFILE)"
    return 1
fi

/etc/config/ddns

config ddns 'global'
    option ddns_dateformat '%F %R'
    option ddns_loglines '250'
    option ddns_rundir '/var/run/ddns'
    option ddns_logdir '/var/log/ddns'

config service 'your_domain_com'
    option lookup_host 'your.domain.com'
    option domain '1325552'
    option password 'your_token_goes_here'
    option param_opt '21694203'
    option update_script '/usr/lib/ddns/update_linode_com_v4.sh'
    option interface 'wan'
    option ip_source 'network'
    option ip_network 'wan'
    option use_https '1'
    option use_syslog '1'
    option cacert '/etc/ssl/certs'
    option use_ipv6 '0'
    option check_interval '1'
    option check_unit 'hours'
    option enabled '1'