I agree, BGP is important to route the IP's, but I've been exploring this same option with a different thought. I'd like to hear what others say about this!
Here is my plan (although not implemented or tested) for Web Services.
At our main data center we have the primary DNS server and our primary web server. The remote location houses the secondary DNS server and our secondary web server. Also at that second location is "hidden" master DNS server. Your registrar name records only point to the primary and secondary, therefore, the internet knows nothing of the hidden master. Then, the hidden master contains a similar set of DNS records that point to the secondary site. Here's the trick! The secondary DNS server syncs with the primary DNS server every x minutes. If the secondary DNS server cannot communicate with the primary DNS server, it then looks at the "hidden" master DNS server and syncs the records (which is pointing at your secondary site). Then, when your data center site comes back up, the secondary tries to communicate with the true master DNS server...it can...therefore it updates its records.
That is the theory in a nutshell. I've read that this is possible, but I haven't had a chance to test it.
What do others think about this? This is no substitution for BGP, but for those that don't run BGP or need to re-route the IP networks, this may work.
--Todd
-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Bryan J. Smith Sent: Thursday, January 05, 2006 12:22 AM To: CentOS mailing list Subject: Re: [CentOS] High Availability using 2 sites
Tim Edwards tim@registriesltd.com.au wrote:
We currently have a backup site at a different location to our main site. This backup site mirrors (as closely as possible) our main services, particularly web serving. Is there a way to have the backup site act as a failover for the main site using something like Linux-HA? They are on seperate internet connections with different IP ranges.
Yes and no.
Yes in that you have a couple of options -- one common, one pretty much a hack.
The common one is to have your own autonomous system number and run BGP. That way you control your IP assignments, failover, etc... in ways that are efficient and quickly propogated.
The hack is to put routers and/or 1-to-1 NAT devices at each site, which can redirect traffic to the other site. That is less efficient and can cause some headaches.
No in the fact that there's really no "software" or "service" facility to deal with this. Round robin DNS does nothing to solve this. Name propogation is always an issue.
So it's something you can only address at the IP-level -- either by having your own, Internet-recognized autonomous system number, or redirecting IPs from each site to the other when servers/sites go down.