Load Balancing Web Applications
Subject:   Load Balancing
Date:   2005-01-03 07:27:47
From:   rboatwright
These are some really odd comments in this forum. I agree this is a great intro into load balancing. Many are asking questions about hardware based load balancing failover. You can use a combination of DNS RR an hardware loadbalancer. So you can get say 3 hardware based load balancers that sit in a DNS RR. Each of the hardware based loadbalancers can have say 6 hosts attached to them. The hardware based loadbalancers will balance to the hosts and the DNS RR will hand out the virtual IPs for the hardware based loadbalancers. If you have 3 hardware based loadbalancers in your DNS RR and one fails, then 1 out of every 3 requests will fail. This is better than a total outage, but still does not prevent users from seeing it when a loadbalancer fails. To get around the DNS RR, you will need to use a global server loadbalancing solution. This is a DNS/Hardware based mix that will act as an authortative DNS for your load blancers, the loadbalancers can send stats back to GSLB and add and remove failed loadbalancers so the end user does not see a failure. Generally the GSLB implementations are high end and very redundant, so the likelhood that it will fail completly is far less than losing a loadbalancer in a DNS RR and having 1/3 of your requests fail. I was reading this article for some knowledge on setting up Tomcat clustering. I have the webservers balanced fine, but if tomcat dies on a server, I lose users and a have a weserver that is still taking traffic for an application server that is not servicing requests. So clustering tomcat is that last step in building a fully redundant and scalable application server farm for me.

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