Camelspotting

So, I spent the greater part of this Saturday on enabling Apache to pass on certain requests to my Apache Tomcat server. Firstly, this was done on FreeBSD 7.2, but I’ll try to keep this at a more generic level. And also I’ll keep it high level as this is not a HOW-TO for either web server.
The software we will be needing:

• Apache 2.2 – FreeBSD port www/apache22 – Documentation
• Apache Tomcat 6.0 – FreeBSD port www/tomcat6 – Documentation
• mod_jk – FreeBSD port www/mod_jk-apache2 – Documentation

So, the gist of the thing is to configure the bridge between the two Apache’s so let’s get to it. Before you read on, I am aware that it is possible to let Tomcat generate the mod_jk.conf-file and I’ll get to that further down.

Apache Tomcat

The part of your Tomcat configuration in which we’re interested is in $TOMCAT_HOME/conf/server.xml. The service that you would like to connect to will need the following connector directive which is the actual entry point for Apache (I’ve also included a virtual host which we’ll match in the Apache config later):

<Connector port="8009" protocol="AJP/1.3" />

<Host name="openttd.camelspotting.com" appBase="/path/to/tomcat/webapps/openttd"
 unpackWARs="true" autoDeploy="true"
 xmlValidation="false" xmlNamespaceAware="false" />

Apache

First we will need a worker. Think of him as the one who’ll carry the requests across the bridge and return the responses. Create a file called worker.properties. You can put this file wherever you want but usually it’s practical to put it next to your httpd.conf file, i.e. $APACHE_HOME/worker.properties. Example content:

workers.tomcat_home=/usr/local/apache-tomcat6.0
workers.java_home=/usr/lib/diablo-jdk1.6.0
worker.list=default
worker.default.type=ajp13
worker.default.host=localhost
worker.default.port=8009

So here you see: I’ve used port 8009  (the default ajp13 port). This has to match the port in the connector described above. Also, notice that the worker is called default. For more details on this file, check out the official documentation. Next, notice that my servers are running on the same host; hence the localhost value for the host property.

All right, final bit of configuration now: create a file (usual name mod_jk.conf) and put it somewhere (usually alongside httpd.conf). Example content:

JkWorkersFile "/usr/local/etc/apache22/workers.properties"
JkLogFile "/var/log/httpd/mod_jk.log"

JkLogLevel emerg
<VirtualHost openttd.camelspotting.com>
    ServerName openttd.camelspotting.com
    JkMount /* default
</VirtualHost>

As you see, the first line defines the worker-file you created previously, so change this to your own setup if necessary. The important thing to notice, though, is the JkMount-directive. The second argument is ajp13 which, you’ll remember, is our worker. Now, add the following line to your httpd.conf:

Include /usr/local/etc/apache22/mod_jk.conf

As usual, modify this path to match your setup. Remember to verify that the jk module is loaded in httpd.conf. It usually looks something like this:

LoadModule jk_module          libexec/apache22/mod_jk.so

The final step is to check your httpd.conf syntax and load the new configuration in some way (start/restart/graceful).

Apache Tomcat mod_jk.conf automatic generation

Tomcat can be configured to generate mod_jk.conf automatically such as to avoid having to edit it every time you change something in Tomcat. This is done by including the following line inside the engine-tag inside your service-tag of server.xml.

<Listener className="org.apache.jk.config.ApacheConfig"
     modJk="/usr/local/libexec/apache22/mod_jk.so"
     workersConfig="/usr/local/etc/apache22/workers.properties" />

By now, these attributes should be self-explanatory. When Tomcat is started it proceeds to generate the mod_jk.conf-file automatically which can then be included into httpd.conf. Sounds great! Well, I could not get that to work at all. The problem is that the generated file does not include any JkMount /* default directives. Please, if someone could tell me what I’m doing wrong, I’ll be thoroughly grateful.