Chapter 2. Load balancing with the Apache Tomcat connector (mod_jk)

Procedure

1. Go to the Apache HTTP Server configuration directory:

   • If you are using the JBCS Apache HTTP Server, go to the JBCS_HOME/httpd/conf.d directory.
   • If you are using the RHEL Apache HTTP Server, go to the /etc/httpd/conf.d directory.

2. Create a new file named mod_jk.conf and enter the following configuration details:

   # 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.d/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 SSL 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
       Require ip 127.0.0.1
   </Location>

   Important

   Ensure that the LoadModule directive references the mod_jk native binary that you have installed.

   Note

   The JkMount directive specifies the URLs that the Apache HTTP Server can forward to the mod_jk module. Based on the configuration for the JkMount directive, mod_jk forwards the received URL to the correct servlet containers.

   To enable the Apache HTTP Server to serve static content (or PHP content) directly, and only use the load balancer for Java applications, the preceding configuration example specifies that the Apache HTTP Server sends only requests with the URL /application/* to the mod_jk load balancer.

   Alternatively, you can configure the Apache HTTP Server to forward all URLs to mod_jk by specifying /* in the JkMount directive.

3. Optional: To use the JkMountFile directive to specify the configuration file for a mount point, perform the following steps:

   1. Go to the Apache HTTP Server configuration directory:

      • If you are using the JBCS Apache HTTP Server, go to the JBCS_HOME/httpd/conf.d directory.
      • If you are using the RHEL Apache HTTP Server, go to the /etc/httpd/conf.d directory.
   2. Create a file named uriworkermap.properties.

   3. Specify the URL that you want to forward and the worker name.

      For example:

      # Simple worker configuration file
      
      # Mount the Servlet context to the ajp13 worker
      /application=loadbalancer
      /application/*=loadbalancer

      Note

      The required syntax is in the format: /URL=WORKER_NAME

      The preceding example configures mod_jk to forward requests for /application to the JBoss Web Server Tomcat back end.

   4. In the mod_jk.conf file, enter the following directive:

      # 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.d/uriworkermap.properties

4. Optional: To enable Apache HTTP Server logging, perform either of the following steps:

   • Include %w in your JkRequestLogFormat directive, as shown in the preceding step about mod_jk.conf settings.
   • Log the name of the mod_jk worker that you want to use, by including %{JK_WORKER_NAME}n in your Apache HTTP Server LogFormat(s).

Procedure

1. Go to the Apache HTTP Server configuration directory:

   • If you are using the JBCS Apache HTTP Server, go to the JBCS_HOME/httpd/conf.d directory.
   • If you are using the RHEL Apache HTTP Server, go to the /etc/httpd/conf.d directory.
2. Create a file named workers.properties.

3. Enter the following configuration details:

   # Define list of workers that will be used
   # for mapping requests
   worker.list=loadbalancer,status
   
   # Define Node1
   # modify the host as your host IP or DNS name.
   worker.node1.port=8009
   worker.node1.host=node1.mydomain.com
   worker.node1.type=ajp13
   worker.node1.ping_mode=A
   worker.node1.lbfactor=1
   worker.node1.secret=<YourSecret>
   
   # Define Node2
   # modify the host as your host IP or DNS name.
   worker.node2.port=8009
   worker.node2.host=node2.mydomain.com
   worker.node2.type=ajp13
   worker.node2.ping_mode=A
   worker.node2.lbfactor=1
   worker.node1.secret=<YourSecret>
   
   # Load-balancing behavior
   worker.loadbalancer.type=lb
   worker.loadbalancer.balance_workers=node1,node2
   worker.loadbalancer.sticky_session=1
   
   # Status worker for managing load balancer
   worker.status.type=status

   Note

   In the preceding example, ensure that you replace host, port, and secret settings with values that are relevant for your environment.

   Important

   The secret property is required when using the Tomcat AJP Connector. You can specify the secret property for a worker node or a load balancer in the workers.properties file. For example:

   worker.<WORKER_NAME>.secret=<YOUR_AJP_SECRET>

   In the preceding example, replace <WORKER_NAME> and <YOUR_AJP_SECRET> with values that are relevant for your environment.

Procedure

1. On the JBoss Web Server host, to configure a unique value for the jvmRoute attribute in the Engine of each worker node:

   1. Open JWS_HOME/tomcat_<VERSION>_/conf/server.xml file.

   2. Enter the following details:

      <Engine name="Catalina" jvmRoute="node1" >

      Important

      Ensure that the jvmRoute attribute value matches the worker name that you specify in the workers.properties file on the Apache HTTP Server host.

2. On the Apache HTTP Server host, to specify the secret property for a worker node or a load balancer:

   1. Go to the Apache HTTP Server configuration directory:

      • If you are using the JBCS Apache HTTP Server, go to the JBCS_HOME/httpd/conf.d directory.
      • If you are using the RHEL Apache HTTP Server, go to the /etc/httpd/conf.d directory.
   2. Open the workers.properties file.

   3. Ensure that the secret property is specified in the following format:

      worker.<WORKER_NAME>.secret=<YOUR_AJP_SECRET>`

      Note

      Ensure that you replace <WORKER_NAME> and <YOUR_AJP_SECRET> with values that are appropriate for your environment.

      Note

      If you set a secret on a load balancer by using the ProxyPass directive, all members of the load balancer inherit this secret. For example:

      <Proxy balancer://mycluster>`
          BalancerMember ajp://node1:8009 route=node1 secret=YOUR_AJP_SECRET
          BalancerMember ajp://node2:8009 route=node2 secret=YOUR_AJP_SECRET
      </Proxy>
      ProxyPass /example/ balancer://mycluster/example/ stickysession=JSESSIONID|jsessionid