I have a few questions regarding connecting Tomcat to Apache.
In our system we have a hardware load balancer that talks to our different Tomcat servers, let's say Tomcat1, Tomcat2, Tomcat3 and Tomcat4. We are introducing session replication in it and hence, we are planning to add Apache Web Server in between hardware load balancer and tomcat.
We have tested that it works if we have 1 Apache server or 4 apache servers containing mod_jk module so that Apache can do the session replication between tomcats.
My first question is, can this be done the other way round? Can Apache run in the background and Tomcat stay in between load balancer and apache? I thought it's not possible but I wanted to be sure. In this case load balancer will forward the request to Tomcat and tomcat will forward the request.
If the answer to the above question is NO, in the first case do you prefer 1 apache server bs 2 apache servers vs 4 apache servers? I like the 2 apache approach.
Tomcat doesn't forward to Apache. Apache can forward to Tomcat. If an app needs resources in both Tomcat and Apache, the two servers should be load-balanced separately and Tomcat and Apache would both connect directly to the load balancer.
However, that's usually not a good solution. Better to set up Apache to forward to Tomcat, and connect the load balancer only to Apache.
The Apache/tomcat connector itself supports load balancing, so you can load balance using the hardware to a set of Apache servers which in turn use mod_jk balanced connections to a cluster of Tomcat servers.
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