Just to clarify, I'm looking at this from an application layer Point of View. One of the reasons why I'm looking at it that way, is because Tim said he was looking at LinuxHA..."application level" redundancy that uses IP.
Tim, just to let you know, I don't believe that LinuxHA will work in the way you described, only because of the different IP ranges. It looks like Linux HA wants to take the main machines IP. With them being on 2 separate networks, that wouldn't work. I haven't looked, but you may want to look at some sort of load balancing solution that you can "weight" which server get's the majority of the request. But, this would require clients hitting the load balancer at one of the facilities, therefore defeating your purpose of redundancy...if they can't hit the load balancer, they can't hit the secondary site!
As for Brian's Message:
1) You are right, to a point. I'm not saying that my idea was a replacement for BGP. I even state that by saying "This is no substitution for BGP".
2) You are correct in saying that you need to change in how the world sees you (whether that be in the application or layer3 routing). That can be done at the application layer or at layer 3. But, if you are a small company that has only 1 internet link at your primary site and 1 internet connection at your remote site and you rely on the internet for communications between the sites, then you technically do not qualify for an AS number. That makes BGP useless. That makes your solution be somewhere in the upper layer of the OSI model.
3) My idea was more on the lines of internet failure at the primary site and using RRDNS on top of that. If the secondary DNS server kicked in and pulled it's configs from the hidden master, then the hidden record wouldn't be configured for RRDNS because it is only used when the primary site fails.
4) My idea was also an application layer solution. Last time I checked, BGP was in Layer 3.
5) Yes, there are some delays when using DNS. Likewise there are delays with BGP. Certainly BGP delays are a lot quicker. No argument there. But again, my idea is looking at it from an application layer POV.
-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Bryan J. Smith Sent: Thursday, January 05, 2006 11:34 AM To: CentOS mailing list Subject: RE: [CentOS] High Availability using 2 sites
Todd Reed treed@astate.edu wrote:
I agree, BGP is important to route the IP's, but I've been exploring this same option with a different thought.
I guess you missed my point. It's _not_ just a matter of using BGP for your dynamic routing. It's a matter of getting an assigned, autonomous system number so the Internet addressing your multiple networks as the same network.
[ There's a lot more to the Internet than just IPs ;-]
That's the proper way to do it.
I'd like to hear what others say about this!
I also made the suggestion to enable 1-to-1 NAT at each facility. Should the servers on one site go down, your 1-to-1 NAT devices would redirect requests to servers at the other site.
That doesn't require an additional, "external" registration/administration. Of course it means packets are now routed to your first site first, then your second site, so if the first site is wiped out (with no equipment), that doesn't help you.
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. .. cut ... That is the theory in a nutshell. I've read that this is possible, but I haven't had a chance to test it.
The problem with the theory is that names are cached all over the Internet. That's why DNS server/name changes don't do squat when it comes to failover.
Now you could _consider_ setting a very low time-to-live (TTL) on your servers -- like 5 minutes. But that doesn't always work either.
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.
Again, it's _more_ than just BGP. ;->
You have to modify how the Internet sees you. Not just what you provide to the Internet. ;->
That's a key distinction that most people don't consider.