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Chapter 2. Apache Tomcat Connector (mod_jk)
The Apache Tomcat Connector, mod_jk, is a plug-in designed to allow request forwarding from Apache HTTP Server to a Servlet container. The module also supports load-balancing HTTP calls to a set of Servlet containers while maintaining sticky sessions.
2.1. Downloading and Installing mod_jk
The mod_jk module is included in the Apache HTTP Server part of a JBoss Core Services installation.
Follow the procedures in the JBoss Core Services Installation Guide to download and install Apache HTTP Server for your operating system.
2.2. Configuring Load Balancing using Apache HTTP Server and mod_jk
You can use the mod_jk connector to configure Apache HTTP Server load balancing. Follow the tasks in this section to configure load balancing using mod_jk, including configuring worker nodes.
Sample configuration files are provided for mod_jk, and are located in JBCS_HOME/httpd/conf.d/. The sample configuration files are: mod_jk.conf.sample, workers.properties.sample, and uriworkermap.properties.sample. To use these samples instead of creating your own configuration files, remove the .sample extension, and modify their content as needed.
Red Hat customers can also use the Load Balancer Configuration Tool on the Red Hat Customer Portal to quickly generate optimal configuration templates for mod_jk and Tomcat worker nodes.
When using this tool for JBoss Web Server 5.1, ensure you select 2.4.x as the Apache version, and select Tomcat as the back-end configuration.
2.2.1. Configuring Apache HTTP Server to load mod_jk
Create a new file
JBCS_HOME/httpd/conf.d/mod_jk.conf, and insert the following configuration:# 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>ImportantThe
LoadModuledirective must reference the mod_jk native binary you installed.NoteThe
JkMountdirective specifies which URLs that Apache HTTP Server will forward to the mod_jk module. Based on the directive’s configuration, mod_jk forwards the received URL to the correct Servlet containers.To enable Apache HTTP Server to serve static content (or PHP content) directly and only use the load balancer for Java applications, the suggested configuration above specifies that only requests with the URL
/application/*are sent to the mod_jk load balancer.Alternatively, you can forward all URLs to mod_jk by specifying
/*in theJkMountdirective.Optional:
JKMountFileDirectiveIn addition to the
JkMountdirective, you can use theJkMountFiledirective to specify a mount point’s configuration file. The configuration file contains multiple URL mappings for Tomcat forwarding.-
Navigate to
JBCS_HOME/httpd/conf.d/and create a file nameduriworkermap.properties. Using the following syntax example as a guide, specify the URL to forward and the worker name.
The syntax required takes the form:
/URL=WORKER_NAMEThe example below configures mod_jk to forward requests for
/applicationto the JBoss Web Server Tomcat backend.# Simple worker configuration file # Mount the Servlet context to the ajp13 worker /application=loadbalancer /application/*=loadbalancer
In
JBCS_HOME/httpd/conf.d/mod_jk.conf, append 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
-
Navigate to
Optional: Configure Apache HTTP Server Logging
You can configure the Apache HTTP Server that is doing the load balancing to log which worker node handled a request. This may be useful when troubleshooting your load balancer.
To enable this for mod_jk, you can either:
-
include
%win yourJkRequestLogFormat(which is configured by default in the suggestion above) ; or -
log the name of the mod_jk worker used by including
%{JK_WORKER_NAME}nin your Apache HTTP ServerLogFormat(s).
For more information on
JkRequestLogFormat, see the Apache Tomcat connector documentation. For more information on Apache HTTP Server logging (including log rotation), see the Apache HTTP Server documentation on log files.-
include
2.2.2. Configuring Worker Nodes in mod_jk
This procedure demonstrates two mod_jk worker node definitions in a weighted round robin configuration with sticky sessions active between two servlet containers.
Prerequisites
-
Understand the format of the
workers.propertiesdirectives. - Configure mod_jk.
To configure mod_jk worker nodes:
-
Navigate to
JBCS_HOME/httpd/conf.d/, and create a file namedworkers.properties. Add the following configuration into
workers.properties, customizing it to your environment:# 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 # 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 # 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
2.2.3. Configuring Tomcat to work with mod_jk
Tomcat is configured to receive AJP traffic from mod_jk by default; however, there is one additional step required before you can use a worker with mod_jk. The AJP connector is configured by default in the JBCS_HOME/tomcat<VERSION>/conf/server.xml:
<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
In addition to the AJP enabled Connector you also need to configure a unique value for the jvmRoute attribute in the Engine of each worker node:
<Engine name="Catalina" jvmRoute="node1" >
The jvmRoute attribute value must match the worker name set in workers.properties.
