Redundancy / Synchronization

I am running a number of Xen PV machines on CentOS 6 (using SolusVM) on a number of physical machines in 3 datacenters.
My client is asking my to provide a redundant solution that his machine is in realtime sync with another at a different datacenter that if his Virtual Machine goes down for any reason the other Virtual machine in a different datacenter is available.
I am not sure how to proceed and will be very thankful for any help.
sysautomationAsked:
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Kent WSr. Network / Systems AdminCommented:
The biggest hurdle here is "what is he syncing"?
Files, database(s)?
Basically you can sync files on a schedule with rsync, databases a few different methods, but step one is get what's needed replicated.
Next you want either a load balancer (haproxy is great and open source), or a DNS failover service like dnsmadeasy.
I use both.
I'd start with DNSME, it's cheap and works great.
If you do a load balancer you would want it to be either at your failover Dc or an independent dc.  Not the same place as your primary server is the key.
With an LB, you also get the benefit of using both servers to double your handling capacity if you want, or just config one as a backup that only gets traffic if your primary is down.
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sysautomationAuthor Commented:
Thanks for the help. The server is running Oracle Express Edition 11g and that's the primary thing to be synced. This version of Oracle does not support sync but some expensive version supports. That's why I thought doing this at VM/OS level. The biggest issue is the customer needs it in real-time and would it be really possible doing it with rsync because of real-time?
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Kent WSr. Network / Systems AdminCommented:
For real time no.  Rsync would not do it.   Unless you were ok with minutes behind.  It's sure cheap if a few minutes aren't a deal breaker.  
DRDB offers block level replication, open source.  Real time replication with buffers / quorum cost quite a bit. Xosoft is thousands.
Neverfail is about the same.
Unless he has a big budget, then block level rep, aside from DRDB, isn't going to be cheap.
If it's *just* the database you need synced, and I'm not big on oracle,  if your version allows it, most databases support the equivalent of master / slave replication.
If that is possible, then you can simply replicate the data to your slave backup, use DNSME or a load balancer for failure detection and failover.
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