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DNS based Website Failover Solutions?
Chase asks: "I run a couple of websites(including for my work). I'd like to have a backup web server that people would hit when my server goes down. My primary host is on my companies T1 line and even though I've had my server die once the most common reason for my sites to be offline is that our T1 goes down. I've looked at the High-Availability Linux Project but it seems that almost everything there is for failover using ip takeover which isn't an option if my network link dies and my backup server is on a different network. ZoneEdit seems to offer what I'm looking for but I'm wanting a do it myself solution. The only software I've found is Eddie and it seems to have stopped development around 2000. I know DNS based failover doesn't give 100% uptime but with a low cache time and decent monitoring it seems like it's the best solution for having my backup server at a differnt location and on a differnt network. Anyone know of a good solution? (Using Linux and/or Solaris hosts)"
Dyndns.org offers free DNS services for dynamic ip addresses. They also offer a fee service that allows you to use your own domain name. Why not set it up with them? If your web server is unreachable by the other server, it will send a dyndns update query with the new address. Just a thought. -P
Read all about IP take over and distributing server load as sample chapter of O'Reilly's Linux Server Hacks.
Don't know if it works for your setup.
My favorite quote:
If you serve a particularly popular site, you will eventually find the wall at which your server simply can't serve any more requests. In the web server world, this is called the Slashdot effect, and it isn't a pretty site (er, sight)
The site is distributed on 4 web servers : 3 on ADSL lines, one on SourceForge. I use 3 independant DNS to announce the web site. On each DNS I also run NAGIOS to monitor each web site. When one of the web site goes down (or up) a special handler (in perl) is called by NAGIOS and dynamicaly update the DNS entry
see global Load balancing for more details and code examples (in french only, but I am working on an English translation).
I set up the DNS TTL to 300 seconds, and NAGIOS can detect a state change in 2 or 3 minutes. So I can have global fail over in less than 10mn.
I have the system running for some month, and it works very well.
It's a king of "poor man's" akamai.
... for a VoIP project. It's a really stupid way of getting very high availability, but it can be made to work, and it is cheap to implement.
Basics are:
(1) you need a heart beat to confirm the master machine is running.
(2) You write a simple script using dnsupdate(8) that removes your master and inserts the backup.
(3) You look up the special magic to tell DNS caching to flush on other machines.