Two mirrored dedicated servers - How? - Knowledgebase

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Two mirrored dedicated servers - How?

Posted by jjviegas, 09-12-2007, 10:28 AM
Hi I have two dedicated servers on two different countries. My idea is having one of them fully active and the other as a backup server so that in case the first crashes or something I only have to redirect the domains to the second server. Can you help me on how this can be done? Thank you in advance
Posted by virtualtoychest, 09-12-2007, 10:57 AM
I am not an expert, but I have been looking into similar issues. There is a program called RSYNC that can be used to keep the backup server up to date. Most DNS services are configured so that you provide several locations. If the first goes down, it will direct your users to the second.
Posted by brianoz, 09-13-2007, 10:34 AM
Almost, sort of. Rsync can be used to synchronize files but it's unlikely it would work well on active databases. You need some sort of MySQL secondary mechanism and MySQL does support something like that. DNS, if given two IP addresses for a host, will hand them out randomly. So some requests will go to the main server, and some to the secondary server. Clearly this isn't what you want for fallback. Another approach is to have a method for changing over the nameservers or IPs if the server fails. One way of doing this is to have the nameservers running on a third, reliable, host. This would detect failure of the other server and substitute in the new IP. About the best you'd get out of this is a 1-2 minute failover, I'd think, and you'd be reliant on ISPs actually obeying DNS cache expiry TTLs and some of them ignore them completely and cache for up to a day. I know there are other techniques but you need to start spending real money to use them; I beleive dedicated hardware is one path people use.
Posted by InfiniteTech, 09-13-2007, 01:56 PM
You will need to use AUX values in such cases. Start reading this article, explains something all those lines... http://support.nerdie.net/index.php?...kbarticleid=50