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18.3. Configure Apache to load mod_jk

Modify APACHE_HOME/conf/httpd.conf and add a single line at the end of the file:

# Include mod_jk's specific configuration file  
Include conf/mod-jk.conf  

Next, create a new file named APACHE_HOME/conf/mod-jk.conf:

# Load mod_jk module
# Specify the filename of the mod_jk lib
LoadModule jk_module modules/mod_jk.so
# Where to find workers.properties
JkWorkersFile conf/workers.properties

# Where to put jk logs
JkLogFile logs/mod_jk.log
# Set the jk log level [debug/error/info]
JkLogLevel info 
# Select the log format
JkLogStampFormat  "[%a %b %d %H:%M:%S %Y]"
# JkOptions indicates to send SSK KEY SIZE
JkOptions +ForwardKeySize +ForwardURICompat -ForwardDirectories
# JkRequestLogFormat
JkRequestLogFormat "%w %V %T"
# Mount your applications
JkMount /application/* loadbalancer
# You can use external file for mount points.
# It will be checked for updates each 60 seconds.
# The format of the file is: /url=worker
# /examples/*=loadbalancer
JkMountFile conf/uriworkermap.properties               

# Add shared memory.
# This directive is present with 1.2.10 and
# later versions of mod_jk, and is needed for
# for load balancing to work properly
JkShmFile logs/jk.shm 
# Add jkstatus for managing runtime data
<Location /jkstatus/>
    JkMount status
    Order deny,allow
    Deny from all
    Allow from

Please note that two settings are very important:

  • The LoadModule directive must reference the mod_jk library you have downloaded in the previous section. You must indicate the exact same name with the "modules" file path prefix.

  • The JkMount directive tells Apache which URLs it should forward to the mod_jk module (and, in turn, to the Servlet containers). In the above file, all requests with URL path /application/* are sent to the mod_jk load-balancer. This way, you can configure Apache to server static contents (or PHP contents) directly and only use the loadbalancer for Java applications. If you only use mod_jk as a loadbalancer, you can also forward all URLs (i.e., /*) to mod_jk.

In addition to the JkMount directive, you can also use the JkMountFile directive to specify a mount points configuration file, which contains multiple Tomcat forwarding URL mappings. You just need to create a uriworkermap.properties file in the APACHE_HOME/conf directory. The format of the file is /url=worker_name. To get things started, paste the following example into the file you created:

# Simple worker configuration file

# Mount the Servlet context to the ajp13 worker

This will configure mod_jk to forward requests to /jmx-console and /web-console to Tomcat.

You will most probably not change the other settings in mod_jk.conf. They are used to tell mod_jk where to put its logging file, which logging level to use and so on.