Tomcat Virtual Hosting

Tomcat virtual hosts are defined inside the Host elements in $CATALINA_HOME\conf\server.xml. $CATALINA_HOME is the tomcat installation directory, hich in my case is /usr/apache-tomcat-5.5.17.
All the Host elements will be enclosed in an "Engine" element. The relevant portion of deafult server.xml is shown below:

<Engine name="Catalina" defaultHost="localhost">
<Realm className="org.apache.catalina.realm.UserDatabaseRealm"
resourceName="UserDatabase"/>
<Host name="localhost" appBase="webapps"
unpackWARs="true" autoDeploy="true"
xmlValidation="false" xmlNamespaceAware="false">
</Host>
</Engine>

Each host element defines a virtual host. To define a virtual host www.myhostingteam.net, we will define a host element as follows.

<Host name="www.myhostingteam.net" appBase="webapps/myhostingteam_net" >
<Context path="" docBase="hostingteam"/>
</Host>

name : The DNS name of the virtual host.

appBase : Application base directory for the virtual host. This directory will hold the web application(s) to be deployed in this virtual host. Path to the directory can be absolute or relative to $CATALINA_HOME.

The "Context" element defines one or more web application contexts defined for this virtual host. There should be atleast one context defined.

path : context path of the web application, which will be matched against the URI request. If left blank, that context will be the default web application for the particular virtual host.

docBase : Document Base/Context Root for the web appliation. This can be either the directiry containing the web application or path to the the web archive (WAR) file for that application. Th e path can be absolute or relative to "appBase" of the virtual host.

Considr the following example:

<Engine name="Catalina" defaultHost="myjavanet.com">

<Host name="www.myjavanet.com" appBase="webapps/myjavanet_com" >
<Context path="" docBase="."/>
</Host>

<Host name="www.myhostingteam.net" appBase="webapps/myhostingteam_net" >
<Context path="" docBase="hostingteam"/>
<Context path="/special" docBase="special_packages"/>
</Host>

</Engine>

Here we have defined two virual hosts, www.myjavanet.com & www.myhostingteam.net

Host www.myjavanet.com: The base directory that holds web applications is /usr/apache-tomcat-5.5.17/webapps/myjavanet_com. There is only one "Context" element, so only one web application is deployed for this host. The "path" attribute is blank indicating that this context is the default context for www.myjavanet.com . The docBAse is ".", means current directory, so the web application is directly deployed inside the appBase Deirectory, which is /usr/apache-tomcat-5.5.17/webapps/myjavanet_com in this case.

Host www.myhostingteam.net : The base directory for web applications is /usr/apache-tomcat-5.5.17/webapps/myhostingteam_net. It holds two web applications, which are deployed in the directories hostingteam and special_packages (docBase) under the "appBase" /usr/apache-tomcat-5.5.17/webapps/myhostingteam_net. The context hostingteam can be accessed with URL http://www.myhostingteam.net, where as special_packages can be accessed with http://www.myhostingteam.net/special (path="/special").

The defaultHost attribute of the Engine element specifies the default virtual host of the tomcat server( if host name in an HTTP request to this server do not match any of the configured virtual host's name attribute, the contents of this virtual host will be supplied instead). This value should match the name attribute of any one of the virtual hosts configured. The default value for this attribute is "localhost".

Multiple DNS names for a single virtual host

Sometimes, you will need to access your site with more than one DNS name, like:
www.myhostingteam.net & hostingteam.net. In such a situation, use the "Alias" element inside the "Host" element.

<Host name="www.myhostingteam.net" ............... >
....................................
<Alias>myhostingteam.net</Alias>
................................
</Host>

You can have any number of <Alias> elements inside a <Host> element.