I have installed Hudson using apt-get, and the Hudson server is available on example.com:8080.

For example.com I use standard port *:80 and some virtual hosts set up this way:

# /etc/apache2/sites-enabled/subdomain.example.com
<Virtualhost *:80>
  ServerName subdomain.example.com
  ...
</Virtualhost>

Here is info about Hudson process:

/usr/bin/daemon --name=hudson --inherit --env=HUDSON_HOME=/var/lib/hudson --output=/var/log/hudson/hudson.log --pidfile=/var/run/hudson/hudson.pid -- /usr/bin/java -jar /usr/share/hudson/hudson.war --webroot=/var/run/hudson/war
  987 ?        Sl     1:08 /usr/bin/java -jar /usr/share/hudson/hudson.war --webroot=/var/run/hudson/war

How should I forward:

    http:// example.com:8080  

to:

    http:// hudson.example.com