First, be a bit more specific. Ultimately, you aren't configuring "a load balancer". You are configuring Ubuntu and some packages, and the end result will hopefully be a system that does load balancing.
What mechanisms and packages are you using as a load balancer? nginx? Or are you using DNS for round-robin load balancing?
Look for cookbooks that help you configure the selected package.
Basically, chef doesn't relieve you from the hard decisions: designing how to accomplish your goal. Arguably, you actually have to do more detailed planning than if you tweak configuration files manually. Chef just helps you deal with the grunt work of fiddling with configuration files, and ensuring that the configuration doesn't get messed up.
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