Comments on: Simply Automating Virtual Machine IP Addressing For Disaster Recovery Sites (without scripting)

By: Nestor Urquiza

Nestor Urquiza — Fri, 01 Jul 2011 20:08:00 +0000

Hi,

Wouldn’t be simpler just to replicate VMs as they are (same Ip/hostname) in DR?

IMO DR should be a dark environment and it should be only turned on when Production is not running.

So I am wondering if someone has experienced with this: SAN to SAN replication to DR and zero reconfiguration to get DR up and running.

Thanks,
-Nestor

By: vCarter

vCarter — Mon, 03 May 2010 20:46:47 +0000

We just finished trying this theory out. We perform 2 offsite DR exercises each year, for different divisions of the company. We have been replicating our vm's, but wanted to simplify even more by using this method. I am pleased to say that this process worked like a charm!

Other than "working as designed", the only issue that we found was that from the primary site, a few of our vm's registered the DR IP address in our primary DNS, which obviously caused problems. We had hoped that changing the binding order of the NICS would resolve this, but it did not. The work-around was to uncheck the default "register in DNS" within the DR virtual NIC advanced properties.

Our process at the secondary site was to turn off the public/production NIC before we powered on the replica, so there would be no conflicts. Just turned the replica on, registered the DR IP, and all worked great!

Thanks again for this suggestion, it is now a part of our documented process.

By: rbrambley

rbrambley — Tue, 02 Mar 2010 17:27:59 +0000

Andy,

Thanks! That sounds like another great alternative for simplifying the
switch to a DR site.

By: Andy Knight

Andy Knight — Tue, 02 Mar 2010 16:43:36 +0000

why don't you use DHCP on both sites with static reservations for all VM's therefore no matter which site you rVM runs on it always comes up with the right Ip details corresponding to the site it is on.

By: Didier Pironet

Didier Pironet — Thu, 14 Jan 2010 18:10:41 +0000

And for that I'm using a script that pushes out to all VMs up in DR the new values for DNS, GW and eventually WINS, Search Order and so on.
Here is a sample script for whom might be interested:
$lines = $(get-content "c:DRServersNewDNS.in")
$backendDNS = "xxx.xxx.xxx.xxx","yyy.yyy.yyy.yyy"
$frontendDNS = "zzz.zzz.zzz.zzz"
foreach ($line in $lines) {
$parts = $line.Split(",",[StringSplitOptions]::RemoveEmptyEntries)
$strComputer = $parts[0]
$strComputer = $strComputer.TrimEnd()
$colItems = get-wmiobject -class "Win32_NetworkAdapterConfiguration" `
-computername $strComputer | Where{$_.IpEnabled -Match "True"}
foreach ($objItem in $colItems) {
if ($objItem.IPAddress -match "^xyz.abc"){
$objItem.SetDNSServerSearchOrder($backendDNS)
}else{
$objItem.SetDNSServerSearchOrder($frontendDNS)
}
}
}

By: Dracolith

Dracolith — Thu, 14 Jan 2010 00:28:26 +0000

This is possibly where something like Cisco DCI comes in:
http://www.cisco.com/en/US/prod/collateral/swit…

I believe VMware validated some L2 bridging scenarios for long-istance VMotion in VSphere, some time ago, under certain latency requirements..
Perhaps long range VMotion under those scenarios could be the all-encompassing DR solution, if you can [one way or another] solve the problem of seamlessly switching over storage to the VM's NFS mount on the DR NAS…..

Otherwise L2 bridging might be _too much_ of a connection between DR and main site.
better use something like Datacenter Bridging, or a L2 bridging loop / broadcast storm could kill both primary and secondary sites….

There's the question of what happens if you need a partial failover?

Better have a fair amount of bandwidth between the two sites, with redundant connections, for inter-VM traffic…

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By: roadfox

roadfox — Wed, 13 Jan 2010 20:35:31 +0000

It might work if you could “switch off” the switch after all is configured. So on Primary Site the DR Switch would be off, and on the DR Site the Primary is off. This way the links of the according interfaces would be down, and no default gateway routing would happen over the “link down” interfaces.

Your next problem is then DNS resolution, if you are using hostnames and not direct ip's.