Failover for business continuity

[Blake Hudson]

Ram wrote the following on 5/30/2012 8:53 AM:
>
> On 05/30/2012 02:26 PM, Eric Luyten wrote:
>> On Wed, May 30, 2012 9:24 am, Ram wrote:
>>> On 05/30/2012 12:43 PM, Dmitry Banschikov wrote:
>>>
>>>> On 05/30/2012 10:52 AM, Ram wrote:
>>>>
>>>>> I am trying to setup a remote cyrus-replica to a different geographical
>>>>> location for business continuity.
>>>>>
>>>>> In case the main server goes down the users will get switched to the
>>>>> remote server by making a DNS change. The only issue is DNS replication
>>>>> would take a long time so the switch is not instantaneous. How would one
>>>>> make the switch instantaneous ? Moving the IP is not possible because the
>>>>> Remote server is on a different network
>>>>>
>>>>>
>>>> You can set TTL of RR to very small value (say 60 seconds). In this
>>>> case, DNS change will be propagated fast.
>>>>
>>>>
>>> But I have seen some DNS clients , especially on windows , do not honor
>>> TTL.
>>> For a 10 minute TTL , even after 4 hours the windows server keeps
>>> resolving to the old server
>> Ram,
>>
>>
>> Correct.
>> Some OSes/applications/resolver libraries will keep on using the 'old'
>> values until *they* see fit.
>>
>> DNS-based failover is (and always has been) a very low cost, halfbaked
>> solution. Been there, done that...
>>
>>
>> Eric.
> So if not DNS based fail over , what is the other alternative.
> I cant move the IP , or re-announce BGP
> I cant have both servers in active-active mode
>

You could use a VPN to easily move the IP address from one location to 
another. This could be accomplished in several ways: a site-to-site L2 
VPN allowing the use of a single subnet at both locations; an imap 
server to router VPN allowing whichever server has an active VPN 
connection to assume the "active" IP; I'm sure there are others.

I would think a VPN would be simpler and thus more reliable than using a 
front end proxy.

--Blake