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Proxying Tomcat with Apache HTTP Server

There is a bunch of step by step tutorials and good references about putting Apache in front of Tomcat around net. Nevertheless, I wrote this article, mainly for myself, in case I come up with same requirement in sometime later.

First, let me give a little background information about problem. We have served JIRA through Tomcat for only our internal use so far. Recently, we have come up with a requirement of letting customers located outside to access JIRA. The network architecture doesn’t allow direct access to internal systems, instead there is a DMZ to put those services which need to be accessed from outside world. However, it was not a wise approach to move JIRA installation to DMZ zone to open it outside world. Therefore, we decided to put an Apache HTTP Server into DMZ and make it forward requests to Tomcat instance running in internal network. Hence, solution will be built upon Apache 2.2.x and Tomcat 6.0.x

In order to integrate Apache with Tomcat, mod_jk module needs to be loaded and configured. Here are the main steps and configuration parts to achieve this.

Configure a Connector with AJP protocol on port 8009 in Tomcat’s server.xml. It’s probably available in the config file but commented, just uncomment it.

<Connector port="8009" enableLookups="false" redirectPort="8443" protocol="AJP/1.3" />

Download mod_jk.so and put it into modules directory of Apache installation. We need to create and configure workers.properties file in order to tell Apache about target Tomcat host and port. There is a full featured and a minimal workers.properties file in source distribution of mod_jk. The minimal configuration was enough for us:

# The workers that jk should create and work with
worker.list=wlb,jkstatus

# Defining a worker named ajp13w and of type ajp13
# Note that the name and the type do not have to match.
worker.ajp13w.type=ajp13
worker.ajp13w.host=jira.hostname.com
worker.ajp13w.port=8009

# Defining a load balancer
worker.wlb.type=lb
worker.wlb.balance_workers=ajp13w

# Define status worker
worker.jkstatus.type=status

Configure Apache to load and run mod_jk module. It is done inside httpd.conf file. However it is better to put those mod_jk specific commands into its own conf file and include it into httpd.conf. That way becomes easier to enable/disable mod_jk by just commenting/uncommenting this include line.

Following piece is from inside newly created httpd-mod_jk.conf file:

# Load mod_jk module
LoadModule    jk_module  modules/mod_jk.so
# Where to find workers.properties
JkWorkersFile E:/work/tools/Apache2.2/mod_jk/workers.properties
# Where to put jk shared memory
JkShmFile     E:/work/tools/Apache2.2/mod_jk/mod_jk.shm
# Where to put jk logs
JkLogFile     E:/work/tools/Apache2.2/mod_jk/mod_jk.log
# Set the jk log level [debug/error/info]
JkLogLevel    info
# Select the timestamp log format
JkLogStampFormat "[%a %b %d %H:%M:%S %Y] "
# Send all requests to worker named wlb
JkMount  /* wlb

You can find detailed information about meanings of those commands in the mod_jk’s development site. You simply load mod_jk module, tell Apache about place of the workers.properties file, and define which requests will be handled by defined workers. Here we forward all incoming requests to the Tomcat instance. It is possible to restrict which requests to be forwarded, and to forward requests to different workers as well.

Following piece is from inside httpd.conf file:

#Tomcat integration
Include conf/extra/httpd-mod_jk.conf

Finally, you just need to restart your Apache and Tomcat instances for changes to take effect.

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