Moving server, keeping hostname and nameservers, changing IP addresses, single server with no DNS clustering

PeteS

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Jun 8, 2017
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I'd like some best practice ideas for how to handle a server move. Currently there is a single cPanel server that has 3 IP addresses (main/shared/hostname, NS1, NS2). The whole server is moving to a new server, which will have a new IP address (could have 3 IP addresses temporarily, by not needed AFAIK, see below). Later the nameservers will be split off to their own DNS Only servers, leaving just the web server, and all will be DNS clustered.

My plan is to configure the new server just as the old, but with the new IP, then transfer accounts and setting as appropriate with the Transfer tool. So far that all has gone will on a test server instance. But I have questions:

1- Am I correct that the new server could be set up using a single IP address used for the main (hostname) IP and for NS1 and NS2? There is no real advantage other than the appearance of redundancy for using 3 IP addresses, AFAIK. (This would only be temporary until the nameservers are split off.)

2- How do I prevent DNS issues from having two servers running concurrently with the same hostname and nameservers but with conflicting IP addresses? Would a solution be turning off PowerDNS on the new server (as I did on the test instance as a precaution) until I want to cut over, then (after short TTLs have propagated from the old server), turn PowerDNS off on the old server and on on the new server?

Or do the glue records at the registrar being set to the old server IP addresses keep things straight, preventing this conflicting info from propagating, and then when I update those records to the new NS IP it will allow the new information? (This doesn't seem like the job of glue records to me, but since the authoritative nameservers are on the same host as each other and the web sites, it's the only unique, non-server provided IP info, so I'm asking.)

3- Wouldn't splitting off the nameservers to 2 DNS Only servers prior to the move, clustering the 2 nameservers instances with the old and new servers, and changing to the new IP addresses in the process be a better strategy? Then I just transfer the accounts with no DNS issues Seems like it would, and would be seamless for account transfers, but...

Splitting off nameservers wasn't part of the initial task - it was added later, and I have never setup DNS clustering and DNS Only servers myself, and though is seems simple enough I don't know what I don't know, AND I am under a time crunch to get the old server moved. For those reasons I didn't initially think in this direction.

Even if the best answer is "Yes, #3!" I would greatly appreciate answers to #1 & #2 also.

Thanks in advance for any help/advice!
 
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cPRex

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Oct 19, 2014
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Hey there! I'll just answer in order to make sure I don't miss anything.

1 - Yes
2 - Nah, that's too complicated I think. I'd do this:

-lower the main TTLs a few days in advance of the migration work
-do the migration
-update the IPs for the nameservers at the registrar
-wait a day or 2
-shut off the webserver (and nameserver if you want) on the Source machine. If the sites continue to work well, you know you're reaching the new Destination system

3 - I like to do as little as possible with each step. I'd do the migration first, make sure everything is working well, then move on to changing up the DNS and cluster settings.
 
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PeteS

Well-Known Member
Jun 8, 2017
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Oregon
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Root Administrator
Well, after writing that up, I told myself to just do it right: #3. :) It's a bit more work up front, but I already was able to get DNS Clustering up and running with two namservers and the old web server. Now I just add the new web server to that cluster, and use the transfer tool to move accounts as I choose. Easy. :)

Question: is there any specific reason to leave the nameserver running on the webserver(s)? Seems like disabling would be best. (web servers have a sync role, nameservers have a standard role)