How to get started with load balancing?

I have an JSP/Servlet web app that runs on one server. While this server holds up for now, I would like to add another server which wil开发者_开发知识库l also give me the advantage of taking one down for maintenance/upgrade etc.

The problem: I have no idea how to do this. How do I get a request that goes to a specific ip to go to two two different boxes depending on the load of the servers?

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You could start with a software load balancer - see HAProxy for an example that's pretty easy to set up.