Sunday, January 25, 2009

Apache in front of Tomcat and JBoss

Recently I have to deploy two Java web applications on a single server (one IP address). Where static content was to be served by Apache Http web server instead of Java application servers. When we have multiple applications deployed on an instance of Tomcat or JBoss we have their URLs something like http://server:port/appA, http://server:port/appB etc. This kind of URLs does not look good when we publish it to external world. So instead of 'http://domainA.tld/appA' we wanted to have URL as 'http://domainA.tld/'. This can be achieved by running applications on different instances of Tomcat / JBoss and fronting them with Apache using virtual hosts.

Running multiple instances of JBoss on a machine with single IP address is a nightmare, while it is much easier to run several Tomcat instances, as one has to change just four ports (8005, 8080, 8443, 8009). An application can be run at root context in Tomcat by adding a line like below, inside <host> element in $TOMCATHOME/conf/server.xml-

    <context path="" docbase="appA.war" unpackWAR="false" />

There are pretty decent documentation available on Apache, Tomcat and JBoss' website about their installation and configuration. So I will leave that discussion here itself. Though there is lots of documentation available for Apache virtual hosting also but it takes lots of effort for a newbie to do the configuration and put it in front of application servers. Here I am assuming that Apache Tomcat Connector (mod_jk) is also installed along with Apache web server.

To establish communication between Apache and application server, first we need to define connector workers as shown below-

    worker.list=appA,appB

    # Define appA
    worker.appA.port=9009
    worker.appA.host=localhost
    worker.appA.type=ajp13
    worker.appA.lbfactor=1

    # Define appB
    worker.appB.port=8009
    worker.appB.host=localhost
    worker.appB.type=ajp13
    worker.appB.lbfactor=1


In the above configuration appA's server's connector is listening on port 9009 and appB's on 8009. This connector port is different from http port (8080 by default for Tomcat). Now define the virtual hosts, this can be done either in Apache's httpd.conf or in a separate file and include that in httpd.conf.

   NameVirtualHost *:80

   LoadModule jk_module modules/mod_jk.so

   # Where to find workers defined above
   JkWorkersFile conf/extra/worker.properties

   <virtualhost *:80>
       ServerAdmin someone@domainA.tld
       DocumentRoot "/path/to/the/content"
       ServerName domainA.tld
       ErrorLog "logs/domainA-error.log"
       CustomLog "logs/domainA-access.log" common

       JkMount / appA
       JkMount /* appA
       JkUnMount /static|/* appA

       JkLogFile logs/mod_jk_appA.log
       JkLogLevel info
       JkLogStampFormat "[%a %b %d %H:%M:%S %Y]"
       JkOptions +ForwardKeySize +ForwardURICompatUnparsed -ForwardDirectories
       JkRequestLogFormat "%w %V %T"
   </virtualhost>

   <virtualhost *:80>
       ServerAdmin someone@domainB.tld
       DocumentRoot "/path/to/the/content"
       ServerName domainB.tld
       ErrorLog "logs/domainB-error.log"
       CustomLog "logs/domainB-access.log" common

       JkMount / appB
       JkMount /* appB
       JkUnMount /static|/* appB

       JkLogFile logs/mod_jk_appB.log
       JkLogLevel info
       JkLogStampFormat "[%a %b %d %H:%M:%S %Y]"
       JkOptions +ForwardKeySize +ForwardURICompatUnparsed -ForwardDirectories
       JkRequestLogFormat "%w %V %T"
   </virtualhost>


With above configuration all requests to domainA.tld are served by worker appA and domainB.tld is served by worker appB. The 'JkUnMount /static|/* appA' causes any URL like http://domainA.tld/static/* to be served by Apache instead of the application server. As Apache performs far better while serving the static content like images, html, css, java script etc. so it is good to unmount their URLs from the mod_jk worker. Most of the Jk* properties can be defined out of the <virtualhost> element at global level, that will avoid duplicate entries. Though defining them inside <virtualhost> element gives flexibility to have different values for each virtual host. Detailed information about Jk* is available here.

I have tested above configuration with following environment-

  • Java: 1.6.0_10
  • Tomcat: 6.0.18
  • JBoss: 5.0.0.GA
  • Apache: 2.2.11
  • OS: Fedora 9, Red Hat Enterprise Linux 5 and Windows Vista
Hope this will be useful to others and save their time.

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