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The mod_proxy_ajp plugin is part of the modern mod_proxy* set of plugins. These have a consistent style of configuration. Implementors with mod_proxy experience will likely favor this plugin. The major concern with this module is it's relative age. There were buggy versions when it first appears around Apache 2.2.3. Sometimes packages are not kept current and these buggy versions may be deployed in your environment. It is suggested to avoid AJP and just use the mod_proxy_http module if mod_proxy* modules will be used.
Mod_Proxy_HTTP
Mod_Proxy_HTTP load balances by directly passing HTTP packets on to the Tomcats. Optionally, HTTPS can be used to encrypt traffic. This approach closely resembles how Tomcats are configured to use hardware load balancers.
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