Chapter 3. Configure Load Balancing Using Apache and mod_jk

Procedure 3.1. Configure Apache to Load mod_jk

1. Open HTTPD_DIST/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
   

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2. Create a new file named HTTPD_DIST/conf/mod-jk.conf
3. Add the following configuration to the mod-jk.conf file.

   Important

   The LoadModule directive must reference the mod_jk library directory location applicable to the native binary you installed.

   Note

   The JkMount directive specifies which URLs Apache should forward to the mod_jk module. Based on the directive's configuration, mod_jk forwards the received URL onto the correct Servlet containers.

   To enable Apache to serve static content (or PHP content) directly, and only use the load balancer for Java applications, the suggested configuration specifies all requests with URL path /application/* are sent to the mod_jk load-balancer.

   If you only use mod_jk as a load balancer, forward all URLs to mod_jk by specifying /* in the directive.

   # 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
    
   # 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 127.0.0.1
   </Location>
   

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4. Optional: JKMountFile Directive

   In addition to the JkMount directive, you can use the JkMountFile directive to specify a mount points configuration file. The configuration file contains multiple Tomcat forwarding URL mappings.
   1. Navigate to HTTPD_DIST/conf.
   2. Create a file named uriworkermap.properties.
   3. Specify the URL to forward and the worker name using the following syntax example as a guide.
      The example block will configure mod_jk to forward requests to /jmx-console and /web-console to Apache.
      The syntax required takes the form /url=worker_name.

      # Simple worker configuration file
      
      # Mount the Servlet context to the ajp13 worker
      /jmx-console=loadbalancer
      /jmx-console/*=loadbalancer
      /web-console=loadbalancer
      /web-console/*=loadbalancer
      

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   4. In HTTPD_DIST/conf/mod-jk.conf, append the following directive.

      # 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

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