Tomcat Virtual Host

4. Configuring Virtual Hosts

The Host element normally needs modification only when you are setting up virtual hosts. Virtual hosting is a mechanism whereby one web server process can serve multiple domain names, giving each domain the appearance of having its own server. In fact, the majority of small business web sites are implemented as virtual hosts, due to the expense of connecting a computer directly to the Internet with sufficient bandwidth to provide reasonable response times and the stability of a permanent IP address. Name-based virtual hosting is created on any web server by establishing an aliased IP address in the Domain Name Service (DNS) data and telling the web server to map all requests destined for the aliased address to a particular directory of web pages. Since this article is about Tomcat, we don't try to show all of the ways to set up DNS data on various operating systems. If you need help with this, please refer to DNS and Bind, by Paul Albitz and Cricket Liu (O'Reilly). For demonstration purposes, I'll use a static hosts file, since that's the easiest way to set up aliases for testing purposes.To use virtual hosts in Tomcat, you just need to set up the DNS or hosts data for the host. For testing, making an IP alias for localhost is sufficient. You then need to add a few lines to the server.xml configuration file:

<Server port="8005" shutdown="SHUTDOWN" debug="0">

  <Service name="Tomcat-Standalone">

    <Connector className="org.apache.coyote.tomcat4.CoyoteConnector"

                       port="8080" minProcessors="5" maxProcessors="75"

                       enableLookups="true" redirectPort="8443"/>

    <Connector className="org.apache.coyote.tomcat4.CoyoteConnector"

                       port="8443" minProcessors="5" maxProcessors="75"

                       acceptCount="10" debug="0" scheme="https" secure="true"/>

      <Factory className="org.apache.coyote.tomcat4.CoyoteServerSocketFactory"

                       clientAuth="false" protocol="TLS" />

    </Connector>

    <Engine name="Standalone" defaultHost="localhost" debug="0">

      <!-- This Host is the default Host -->

      <Host name="localhost" debug="0" appBase="webapps"

              unpackWARs="true" autoDeploy="true">

        <Context path="" docBase="ROOT" debug="0"/>

        <Context path="/orders" docBase="/home/ian/orders" debug="0"

                       reloadable="true" crossContext="true">

        </Context>

      </Host>

      <!-- This Host is the first "Virtual Host": www.example.com -->

      <Host name="www.example.com" appBase="/home/example/webapp">

        <Context path="" docBase="."/>

      </Host>

    </Engine>

  </Service>

</Server>

Tomcat's server.xml file, as distributed, contains only one virtual host, but it is easy to add support for additional virtual hosts. The simplified version of the server.xml file in the previous example shows in bold the overall additional structure needed to add one virtual host. Each Host element must have one or more Context elements within it; one of these must be the default Context for this host, which is specified by having its relative path set to the empty string (for example, path="").