Quick Setup of Tomcat with mod_jk under RedHat 9.0

RedHat Linux comes, like most distributions, shipped with an Apache HTTP Server. When starting on school with classes on Java Server Pages, most people assumed this was going to be done under Windows (a poor man's operating system). Of course I didn't want to give up my free-software position, so I started to look what I needed to do to get JSP pages running under Linux. I browsed to the Jakarta Project (http://jakarta.apache.org/) and looked into installing a Tomcat webserver on my RedHat Linux 9 PC.

Though the first steps where pretty simple, running JSP under my already installed Apache HTTP Server caused me some headaches. At the end I have to say that these headaches were not caused by difficuly installation routines, but more by large amounts of documentation which just didn't get to the point. Below are the steps I took to get it all running. I hope it will turn out easier for you, if you do the same thing.

Note that you can run both Tomcat and Apache HTTP Server on one and the same machine, but you'll need a mod_jk if you want to have communication between both(!) servers and the outside world. Actually only Apache HTTP Server listens to the outside world, while Tomcat listens to Apache.

Setup of Tomcat

• First I made sure I had a Java 2 Software Development Kit installed. Before, I had downloaded one of the prebuild RPMS of Sun (http://java.sun.com/j2se/downloads.html). The RPM I took, installed J2SDK into /usr/java/j2sdk-{versionnumber}.

• Next I set a system variable JAVA_HOME in /etc/profile:
  

  # echo JAVA_HOME=/usr/java/j2sdk-{versionnumber} >> /etc/profile

• I then downloaded a binary version of Tomcat from http://jakarta.apache.org/ (a TAR.GZ file) and unpacked it in /opt. It doesn't really matter where you put it, as long as you remember where :).

• I set a system variable CATALINA_HOME in /etc/profile (Catalina is the servlet container of Tomcat, basically the core):
  

  # echo CATALINA_HOME=/opt/jakarta-tomcat-{versionnumber} >> /etc/profile

• I ran the startup.sh script located in the Tomcat directory
  

  # $CATALINA_HOME/bin/startup.sh

  and pointed my browser to the address http://localhost:8080 and it worked!
  Any JSP file I put now in the $CATALINA_HOME/webapps directory, would appear on the page.

Now the mod_jk module

So far so good, and easy. But I had now two webservers running: Apache listening to port 80 and Tomcat listening to port 8080. It didn't seem to be a good idea to me. So the next thing to do was getting a mod_jk Apache module to load into the Apache server, which passes JSP-requests through to the Tomcat server, which can only be reached internally (localhost).

The Apache server shipped with RedHat 9 is version 2.0.40. I looked around on the Internet, but nowhere I could find a precompiled mod_jk module (mod_jk.so) for this Apache version. Using modules precompiled for other versions, didn't work out either - Apache complained about a wrong version. So I had to compile my own. I had to experience again how wonderfull life with open source software can be.

Many sites (to my own impression even the Jakarta Project itself) make you believe you need Ant to compile the module, or the complete source code of the Apache server (which isn't shipped with RedHat), or a large list of JAR files from both the Jakarta Project. I wanted to keep it simple. At the end, I did.

• I checked if "apxs" (Apache eXtension Tool) was on my system. (apxs is part of the Apache HTTP Server distribution, but is excluded on some Linux distributions. If apxs is missing, you'll probably have to download an Apache HTTP Server distribution from their site.)

  # whereis apxs

  Lucky for me, it was right there on my system.

• I downloaded the Tomcat Connector source package from http://jakarta.apache.org/ (from the same location where we downloaded the Tomcat server), and unpacked it again in /opt. (NOTE: I used the Tomcat BINARY package but the Tomcat Connector SOURCE package.)

• I went into /opt/jakarta-tomcat-connectors-{versionnumber}/jk/native directory and ran

  # ./buildconf.sh

• Next I ran

  # ./configure --with-apxs=/usr/sbin/apxs

  Don't use the --with-apache option. (Later I forgot why. Maybe cause I didn't had the original Apache source on my system, but just the RedHat version.)

• The configure went fine, so I ran

  # make

• Make built a shared library called "mod_jk.so" for me which I then copied to the modules directory of Apache "/etc/httpd/modules/". I made sure the permissions of the shared library where the same as the other modules in this directory (defaults to 755).

• Now the module itself is in place, I needed to tell Apache what to do with it. The Jakarta Project offers a default configuration file, in which I modified the LoadModule statement to point to the "/etc/httpd/modules/" directory. I put the mod_jk.conf file in the "/etc/httpd/conf.d/" directory so it is automatically read by Apache.

  In this configuration file the module (mod_jk) is loaded by Apache. If this goes wrong, it probably means that the module has been compiled in a wrong way.

  Important for the lot to work is the JkMount statement: A worker called "ajp13" is used to forward URI requests stated here, to forward the request to the Tomcat server. Here the magic comes alive. "Ajp13" is a connection handler of Tomcat listening to a default port 8009, connecting Apache to Tomcat.

• The mod_jk.conf file calls another file called workers.properties which I placed as well in the same directory (/etc/httpd/conf.d/). Make sure you change the "workers.tomcat_home" and "workers.java_home" lines in "workers.properties" as well.

Finishing touch

• Restart the Apache daemon:

  # /etc/init.d/httpd restart

  If this fails, it's probably your module's fault.

• In the case of the configuration found in my files, if you request the URL "http://localhost/jsp", Apache connects you through to Tomcat. If this happens, Tomcat should confront you with a PAGENOTFOUND. Now create a directory $CATALINA_HOME/webapps/ROOT/jsp, and you should get an Index listing of your new built directory.

  I just created here a JSP page "index.jsp" (with read permissions for Tomcat) with the following line

  <% out.println("Hello World"); %>

  See if it prints "Hello World".

• It really works!

My own spam-spamming page

The following addresses are spamtraps. Do not use them or you will be banned from hundreds of web sites

Webmaster Editor Sales