how to use mod_jk on centos 6.x

proxy_mod_ajp is the new way to interface Apache with Tomcat (it comes with as the standard module), hence mod_jk is deprecated and can’t be found in repos.

For proxy_mod_ajp this is the way to configure:
<VirtualHost *:80>
<Proxy *>
AddDefaultCharset Off
Order deny,allow
Allow from all

ProxyPass / ajp://localhost:8009/
ProxyPassReverse / ajp://localhost:8009/

But proxy_mod_ajp may not do for you, so this is how to use mod_jk:

yum install httpd-devel

Download latest Tomcat connectors
tar -xzf tomcat-connectors-1.2.37-src.tar.gz
cd tomcat-connectors-1.2.37-src/native
./configure --with-apxs=`which apxs`
make && make install

Add in httpd.conf:

LoadModule jk_module modules/
JkWorkersFile /etc/httpd/
JkLogFile /var/log/httpd/mod_jk.log
JkLogLevel debug

Update your vhost to match:
<VirtualHost *:80>
<IfModule mod_jk.c>
JkMount /*.jsp ajp13
JkMount /servlet/* ajp13
JkMount /servlets/*

Restart Apache.

Alternative solution
Or, better yet, completely avoid going through Apache for java pages.
Install haproxy, configure a frontend for all http traffic, use ACLs to separate normal traffic from java pages and configure two separate backends, one for Apache and the other for Tomcat.

How to add a new vhost in Tomcat