Apparently (hi Zhenech, found on Plänet Debian), a Man does not only need to fork a child, plant a tree, etc. in their life but also write a DynDNS service. Perfect for opening a new tag in the wlog called archæology (pagetable.com – Some Assembly Required is also a nice example for these).
Once upon a time, I used SixXS’ heartbeat protocol client for updating the Legacy IP (known as “IPv4” earlier) endpoint address of my tunnel at home (My ISP offers static v4 for some payment now, luckily). Their client sucked, so I wrote on in ksh, naturally.
And because mksh(1) is such nice a language to program in (although, I only really begun becoming proficient in Korn Shell in 2005-2006 or so, thus please take those scripts with a grain of salt, I’d do them much differently nowadays) I also wrote a heartbeat server implementation. In Shell.
The heartbeat server supports different backends (per client), and to date I’ve run backends providing DynDNS (automatically disabling the RR if the client goes offline), an IP (IPv6) tunnel of my own (basically the same setup SixXS has, without knowing theirs), rdate(8) based time offset monitoring for ntpd(8), and an eMail forwarding service (as one must not run an MTA on dynamic IP) with it; some of these even in parallel.
Not all of it is documented, but I’ve written up most things in CVS. There also were some issues (mostly to do with killing sleep(1)ing subprocesses not working right), so it occasionally hung, but very rarely. Running it under the supervise of DJB dæmontools was nice, as I was already using djbdns, since I do not understand the BIND zone file format and do not consider MySQL a database (and did not even like databases at all, back then). For DynDNS, the heartbeat server’s backend simply updated the zone file (by either adding or updating or deleting the line for the client) then running tinydns-data, then rsync’ing it to the djbdns server primary and secondaries, then running zonenotify so the BIND secondaries get a NOTIFY to update their zones (so I never had to bother much with the SOA values, only allow AXFR). That’s a really KISS setup ☺
Anyway. This is archæology. The scripts are there, feel free to use them, hack on them, take them as examples… even submit back patches if you want. I’ll even answer questions, to some degree, in IRC. But that’s it. I urge people to go use a decent ISP, even if the bandwidth is smaller. To paraphrase a coworker after he cancelled his cable based internet access (I think at Un*tym*dia) before the 2-week trial period was even over: rather have slow but reliable internet at Netc*logne than “that”. People, vote with your purse!