It is a botheration as old as the Internet. You appetite to admission your computer remotely, but it is abaft a router that about gets altered IP addresses. Or maybe it is your laptop and it apprehension up in altered locations with, again, altered IP addresses. There are abounding agency to break this botheration and some of them are bigger than others.
A lot of routers can abode their IP abode to a activating DNS server. That acclimated to be great, but now it seems like abounding of them basset you to advancement or consistently renew so you can see their ads. Some of them disappear, too. If your router bell-ringer food one, that adeptness be a acceptable choice, until you change routers, of course. OpenWRT supports abounding such casework and there are abounding lists of accepted services.
However, if you accept a distinct attainable attainable computer, for archetype a Web server or alike a billow instance, and you are active your own DNS server, you absolutely don’t charge one of those services. I’m activity to appearance you how I do it with an attainable Linux server active Bind. This is a accepted setup, but if you accept a altered arrangement you adeptness accept to acclimate a bit.
There are abounding agency to set up activating DNS if you are accommodating to accept a abundant accord of anatomy on both sides. Most of these depend on ambience up a abstruse key to acquiesce for DNS updates and some array of calligraphy that calls nsupdate or accepting the DHCP server do it. The botheration is, I accept a lot of applicant computers and abounding are set up differently. I capital a arrangement area the alone affair bare on the applicant ancillary was ssh. All the basement charcoal on the DNS server.
I’m activity to accept you already accept Bind bureaucracy and you accept a alive adeptness of what DNS does. In general, though, you will accept a distinct book for anniversary area — area in DNS allege — you control. Here’s a archetypal area book (RFC 1035 controls the format):
The genitalia of absorption actuality are the $TTL or time to live. The amount is in seconds, so this is an hour. That adeptness be a bit continued to delay if your IP abode changes a lot. There’s additionally a consecutive cardinal that servers use to acquaint that the almanac changed. There’s no absolute architecture to the cardinal as continued as every change after-effects in a beyond number. You can use a arrangement adverse or permute the date. It doesn’t absolutely matter. Finally, there are IN annal that acquaint us altered IP addresses. For this file, @ is a autograph for wd5gnr.com and annihilation afterwards a aeon at the end will accept wd5gnr.com added to it. So the aftermost band defines a host “www.wd5gnr.com” and could accept been accounting with “www.wd5gnr.com.” instead of “www” — that aftermost aeon makes all the difference.
Somehow, we charge a way to accomplish added annal in this area book that will point added hosts — maybe dyn.wd5gnr.com — to a altered IP address. I started out with a actual simple calligraphy on the DNS server that would acquisition the IP abode of the accession and adapt a arrangement to actualize a DNS area book and afresh reload the zone. This formed until I capital to handle added than one activating host at a time. I’ll appearance you how I dealt with that, but first, let’s allocution about what you charge to do this yourself.
In accession to the DNS server for a area you control, you’ll additionally charge ssh admission to your server set up to use a affidavit and not a password. You apparently charge basis access, too, although I’ll appearance you how you won’t charge it afterwards setup, if you don’t apperception acceptance anyone logged into your annual to amend your IP address.
Setting up ssh to not crave a countersign is accessible and awful recommended. If you charge a album on ambience up Bind, you can apprehend this article, as continued as you bethink to use your amalgamation administrator in abode of yum — unless your amalgamation administrator is yum! Or you adeptness adopt this one.
Once you accept your DNS server set up and an ssh session, there are alone a few things to setup.
The script, of course, is a Bash calligraphy but it makes acceptable use of Awk. My aboriginal arrangement book architecture was simple. I fabricated a archetype of the area file, alter the consecutive cardinal with $SERIAL and the activating IP abode with $IP. The calligraphy would bung in new ethics and reload the DNS server application a ascendancy affairs accepted as rndc, added in a minute.
The better botheration with this arrangement is that there is alone one activating IP abode allowed. But afore we fix that, let’s attending at some of the problems. First, we charge to apprentice the alien abode of the computer calling the script. Here’s some code:
This, of course, assumes we are logged in via ssh. I took a few shortcuts back I didn’t apprehend to alarm this calligraphy manually except during testing. The arguments were simple, although I’d after accept to add a bit more. The aboriginal calligraphy took an IP abode or a birr to announce my ssh IP address, a area name and that was it.
The calligraphy would attending for ${ZONENAME}.dns.template in the accepted agenda and use a simple awk calligraphy to gsub any accident of $SERIAL and $IP in the template. Awk would abode to a acting book and already successful, I’d move the book over to the DNS book (again, in the aforementioned directory) and accomplish the server update.
That aftermost bit is a little tricky, too. Bind has a tool, rndc, that can reload a area (among added things). But commonly you accept to be basis to run it. You can use sudo, of course, but for an automatic script, that’s not accessible back it will appetite your password.
Turns out that sudo has a lot of appearance you don’t generally use. One of them will acquiesce users or groups of users to assassinate things with no countersign alike if it would commonly crave root. Obviously, you charge to be actual accurate with this ability. I fabricated a book alleged /etc/sudoers.d/91-dynamicdns on the DNS server that has a distinct band in it:
This allows me to reload that one area book as my accustomed user afterwards entering a countersign by application sudo. If you try to do annihilation else, you’ll still get the sudo countersign prompt.
XKCD by [Randall Munroe] CC By_NC 2.5
All that’s larboard is to alarm the calligraphy on the bounded apparatus application ssh. You accept several options. Of course, active it manually is accessible enough, but I acclimated cron or anacron to agenda beheading of the calligraphy periodically and almost in accompany with the TTL value. You could use systemd, if you prefer. On a laptop application NetworkManager, it would be accessible to abode a calligraphy that runs back the arrangement affiliation connects, which would apparently be suitable.
Exactly how you do it will depend on your setup. Keep in apperception that alike already WiFi connects, the router could get a new WAN IP abode at any time, so apparently some array of alternate amend is a acceptable abstraction alike if you appetite to force an amend on arrangement affix or log in.
That all formed accomplished for a while, but I eventually capital to acquiesce for assorted lines. The botheration is that anniversary amend is broken from the rest. Somehow you appetite the arrangement to alone appulse the specific curve that charge to change. I additionally capital to analysis the IP abode and alone reload in the case that the new IP abode was different.
There are abounding solutions to this problem, of course. It would alike be accessible to abundance the IP addresses in a database or book and afresh accomplish all updates anniversary time. But that seemed like a pain, so I autonomous for article easier. The arrangement book will now archetype any band afterwards a prefix appropriate to the achievement unchanged. But some curve will accept a prefix which is argument followed by a colon. Back the calligraphy finds such a line, it looks to see if the prefix is the one we are alive with. If so, it replaces $SERIAL and $IP as before. It strips the prefix off and briefly stashes the line. There is one appropriate prefix, !, that matches any prefix. That’s primarily to acquiesce $SERIAL to be acclimated in one band that changes on anniversary update.
With this new scheme, no achievement occurs as the calligraphy processes the template. However, the calligraphy now takes two arguments: the arrangement and the absolute area file. Processing for the additional book is different. It artlessly copies anniversary band from the area book to a new book unless there was a backup band from the aboriginal pass. If there is, that band replaces the old line. You can actuate which canyon awk is in by attractive at ARGIND which tells you which book you are currently processing.
The alone big issue, then, is if you approved to run the calligraphy alert at the aforementioned time. The acknowledgment to that botheration is to use flock, a address covered in an beforehand Linux-Fu.
You can acquisition the absolute final calligraphy on GitHub forth with an archetype arrangement file. Note that aggregate runs on the server. You artlessly run the calligraphy via ssh — and that can be done automatically in a cardinal of agency — and the cipher on the server ancillary takes affliction of the rest. Back you apparently charge ssh set up anyway, this agency there are no added keys to advance and no updates to anniversary applicant any time you appetite to adapt anything.
As usual, there are abounding agency to break this problem. This may or may not clothing your needs. I advised aloof autograph the arrangement application $INCLUDE to accommodate a sub area book for anniversary activating host and accepting the calligraphy abode those. That will apparently assignment but if you had a lot of hosts, it would wind up with a lot of devious files. There is additionally some ambiguity in RFC 1035 as to the actual behavior of $INCLUDE although the Bind affidavit clears it up, at atomic as far as Bind is concerned.
It still shows some absorbing tricks with awk and flock, though. There are added agency to acquisition your alien servers, such as PageKite. Finally, you can bandy accouterments at the problem.
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