这些模块的优缺点比较存在
http://blog.jboss.org/

mod_proxy

* Pros:
      o No need for a separate module compilation and maintenance. mod_proxy,
        mod_proxy_http, mod_proxy_ajp and mod_proxy_balancer comes as part of 
        standard Apache 2.2+ distribution
      o Ability to use http https or AJP protocols, even within the same 
        balancer.
* Cons:
      o mod_proxy_ajp does not support large 8K+ packet sizes.
      o Basic load balancer
      o Does not support Domain model clustering

mod_jk

* Pros:
      o Advanced load balancer
      o Advanced node failure detection
      o Support for large AJP packet sizes
* Cons:
      o Need to build and maintain a separate module