On Sun, Nov 06, 2005 at 09:48:06PM +1030, Tim wrote: > Tim: > > >> I think that the usefulness of Paul's example is that you can change > >> the machine acting as "myserver" with one record change (the A record > >> for "myserver". Alternatively, if you made all the next three > >> records "A" records with the same IP address, you'd need to change > >> all of them. > > Derek Martin: > > > Oh, come now... > > > > If this is genuinely a problem for you, then you need to spend some > > time learning how to use your favorite editor, or find a better one... > > Re-instating my next paragraph: > > "Probably not a real pain for three servers, but if you'd faced an > annoyance of suddenly having to replace 10, or more, server > addresses in one go, you'd probably appreciate being able to fix > things with just one modification to one record." Sigh... I read this the first time, and it simply isn't true. That's why I left it out. It's irrelevant, because this "annoyance" you speak of is easily eluded... it's a red herring. > It's clear that you're just flapping your gums in the breeze for the > sake of having an argument. NO. THIS IS NOT A PROBLEM. No matter how many servers you're talking about, we're still talking about changing the CNAMEs or A records associated with one machine (or rather, one A record and therefore 1 IP address). THIS CAN ALWAYS BE DONE QUICKLY AND EASILY, if you know how to use the tools at your disposal, whether it's 10 or 10,000 records. > No, it's not something I want to do, but from the theoretical point of > view, there's a good reason for the technique Paul offered of CNAMEing > lots of different servers to the one server address: The simplicity of > changing the lot, in one go, with just one edit, to a different address, > should you need to. And I say it's not a factor at all. I gave you syntax to do exactly that (change them all with one edit), assuming they're all in one file. If the addresses are in different files, you have a couple of options. If you have some aversion to shell scripts, you can load them all into your editor at the same time, in different buffers, and just repeat the search and replace operation once per buffer. Or if that's too much work for you, you can use a tiny shell script to do it on the command line. I don't care if you have 1,000,000 records that all point to the same IP address. This just simply IS NOT A PROBLEM. > There is really no argument to say that it's not easier to just edit the > one A record to change where all the CNAMEs point to, compared to > writing a script just to do the same thing. It takes 5 minutes to write the script, and once it's done you never need to do it again. So every time other than the first time, THERE IS NO DIFFERENCE. And to save you the trouble of writing the script the first time, here it is: -=-=-=-=- #!/bin/sh # ip_fixer.sh - change IP of all A records that point to $1 # $1 is the old IP, $2 is the new IP # # This is untested due to lack of any zone files on my machine to test # them with (and sheer laziness to grab some), though I think it's # right. If it is somehow broken, it should be simple to fix with a # few minutes of testing. # # This really should save back-up copies of the originals and use # mktemp for security, but who cares? It's just a quick and dirty # hack to prove a point anyway. # TMPFILE=$TMPDIR/mytmpzone regex=`echo $1 | sed 's/\./\\./'` for file in *; do if grep -q "[^0-9]$regex[^0-9]" "$file"; then sed "s/[^0-9]$regex[^0-9]/$2/g" > "$TMPFILE" mv "$TMPFILE" "$file" fi done rm $TMPFILE -=-=-=-=-=- There. 9 lines of code plus comments. The comments took more time to write than the script itself... Now you never have an excuse not to use A records instead of CNAMEs. Run this script in the directory where you keep your zone files, and you never have to change them manually again. I would argue that this is actually EASIER than changing just one A record to which many CNAMEs point, because you don't need to know what file the A record lives in, and you don't have to load it up in your editor and search for it. You only need to type one line: ip_fixer.sh <old_IP> <new_IP> and the whole thing is done. No editing necessary. How much easier could it possibly be? As an extra added bonus, it will even work for partial IPs (assuming it works at all), say if you want to change your subnet from 172.16.7 to 10.1.3. If you're a little bit clever, it's easy to modify it to automatically update your zone files' serial numbers too. I'll leave that as an exercise. [Hint: since it's just a series of decimal digits, you need something to help match on the serial number in the zone file, so a well-placed comment would be quite useful (e.g. ; Serial Number.).] After that, you can even have it tell named to reload the zone files for you... Simplicity itself. Now I admit, this is not as helpful if only SOME of your hostnames need to change... but CNAMEs won't help you much there, either. You'll still need to change all the CNAME records that are going to point to a different machine, and unless you have some clever naming scheme that you can match on, you're going to need to do that entirely by hand to make sure you get it right (same as with A records)... And don't forget about all the problems we mentioned before that CNAMEs can potentially cause. CNAMEs are NOT better, IMO, not in any way. They SEEM like a good idea, but their implementation can cause problems which are not worth the hastle. -- Derek D. Martin http://www.pizzashack.org/ GPG Key ID: 0x81CFE75D
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