[CentOS] Replacing Multiple Servers with One

Les Mikesell
2013-03-06T17:12:41Z

On Wed, Mar 6, 2013 at 10:40 AM, Tim Evans <tkevans at tkevans.com>
wrote:
> We are replacing four servers, running mail, web, ftp, and dns,
> respectively, with a single server to run all four services.
>
> The new server will have a new IP address.
>
> It seems fairly straightforward to redirect mail, web, and ftp services
> to the new server via DNS CNAMES,

SMTP mail needs to use MX records, not CNAMEs, and in fact the target
of the MX can't be a CNAME.    Pop/imap connections want an A record
or CNAME.    You can use multiple MX records and they don't all have
to work - smtp deliveries are supposed to try them all before failing
so that can be handy during transitions.

>but I'm not quite sure about how to do
> the change for the DNS service itself.

> Is there a need to maintain the old DNS server's IP address during a
> transition, or longer? Via a virtual IP with the old DNS server's IP
> address on the new machine, perhaps? Or a second NIC with the old
> address? Or just have the router redirect incoming DNS requests?

Is this a 'public' DNS server?  These must be registered (and there
should be at least 2 so you can move them and the registration one at
a time).  Or a local resolving server?   These have the IPs configured
into every client and/or will be handed out via DHCP.   Again, there
should be at least 2 but failures cause fairly long timeouts so
breakage is a bad thing.    Assuming these are all in the same subnet,
the simple fix is to use IP aliases to keep the old addresses on the
new server until you are sure that everything knows the new one.
More drastically, but sometimes easier, you could also convert the old
machines to VMs running on a single physical host which would let you
consolidate the hardware without many logical changes.

--
   Les Mikesell
     lesmikesell at gmail.com