I know how to run two or more tomcats under one apache server. I want to know how to run two or more apache servers in a cluster and run my application. I know it's possible. can someone suggest a simple tutorial? there are many articles for apache - tomcat integration, but not for apache clustering. :( it would be great if you guys suggested a basic tutorial. thanks.
get a software or hardware load balancer and put it in front of the apache servers.
1) install free load balancer: "balance" from http://www.inlab.de/balance-3.42.tar.gz
2) run: balance -f 80 server1:80 server2:80 server3:80
advanced tutorial: The problem with the solution above is that it introduces a single point of failure. If your "balance" server dies, then you cannot access anything behind it.
If you want to go with a home grown solution GPL, then you need to run "vvrpd", "heartbeat" or some other failover cluster solution (or google: linux load balancing).
If you want to stay with a software solution, but have money, you could look at Redat Cluster, Veritas Cluster, or some other vendors cluster software.
Your best/most reliable solution though is to get a pair of hardware load balancers (which will do failover automatically).
I'm assuming that you want to run this on multiple machines (running multiple Apache instances on the one machine makes very little sense).
Unfortunately, you can't find a simple tutorial for HA clustering because it's not a simple topic. You've got a lot of different concepts, ranging from low-level network stuff to application-specific items like shared data storage.
I started my clustering adventures at http://linuxvirtualserver.org/. You might like to start at http://www.linuxvirtualserver.org/architecture.html and go from there.