@@ -1460,9 +1460,10 @@ System Configuration
* Customizing the Kernel:: Creating and using a custom Linux kernel on Guix System.
* Guix System Image API:: Customizing images to target specific platforms.
* Using security keys:: How to use security keys with Guix System.
+* Dynamic DNS mcron job:: Job to update the IP address behind a DuckDNS host name.
* Connecting to Wireguard VPN:: Connecting to a Wireguard VPN.
* Customizing a Window Manager:: Handle customization of a Window manager on Guix System.
-* Running Guix on a Linode Server:: Running Guix on a Linode Server
+* Running Guix on a Linode Server:: Running Guix on a Linode Server.
* Setting up a bind mount:: Setting up a bind mount in the file-systems definition.
* Getting substitutes from Tor:: Configuring Guix daemon to get substitutes through Tor.
* Setting up NGINX with Lua:: Configuring NGINX web-server to load Lua modules.
@@ -2022,6 +2023,59 @@ Using security keys
ready to be used with applications supporting two-factor authentication
(2FA).
+@node Dynamic DNS mcron job
+@section Dynamic DNS mcron job
+
+@cindex dynamic DNS, DDNS
+If your @acronym{ISP, Internet Service Provider} only provides dynamic
+IP addresses, it can be useful to setup a dynamic @acronym{DNS, Domain
+Name System} (also known as @acronym{DDNS, Dynamic DNS}) service to
+associate a static host name to a public but dynamic (often changing) IP
+address. There are multiple existing services that can be used for
+this; in the following mcron job, @url{https://duckdns.org, DuckDNS} is
+used. It should also work with other dynamic DNS services that offer a
+similar interface to update the IP address, such as
+@url{https://freedns.afraid.org/}, with minor adjustments.
+
+The mcron job is provided below, where @var{DOMAIN} should be
+substituted for your own domain prefix, and the DuckDNS provided token
+associated to @var{DOMAIN} added to the
+@file{/etc/duckdns/@var{DOMAIN}.token} file.
+
+@lisp
+(define duckdns-job
+ ;; Update personal domain IP every 5 minutes.
+ #~(job '(next-minute (range 0 60 5))
+ #$(program-file
+ "duckdns-update"
+ (with-extensions (list guile-gnutls) ;required by (web client)
+ #~(begin
+ (use-modules (ice-9 textual-ports)
+ (web client))
+ (let ((token (string-trim-both
+ (call-with-input-file "/etc/duckdns/@var{DOMAIN}.token"
+ get-string-all)))
+ (query-template (string-append "https://www.duckdns.org/"
+ "update?domains=@var{DOMAIN}"
+ "&token=~a&ip=")))
+ (http-get (format #f query-template token))))))
+ "duckdns-update"
+ #:user "nobody"))
+@end lisp
+
+The job then needs to be added to the list of mcron jobs for your
+system, using something like:
+
+@lisp
+(operating-system
+ (services
+ (cons* (service mcron-service-type
+ (mcron-configuration
+ (jobs (list duckdns-job ...))))
+ ...
+ %base-services)))
+@end lisp
+
@node Connecting to Wireguard VPN
@section Connecting to Wireguard VPN