Until last week I thought it would be necessary to configure Tomcat and its webapps as a big monolithic system. What a great mistake! I have learned that there is a much easier way to run webapps in Tomcat. Actually each webapps becomes its own application server, executed with a dedicated user. I will demonstrate this way by showing how to install Jenkins.

First install Java JDK and Tomcat into /opt. In this case, I have just unpacked the tarballs there and created symlinks to have an easy way to upgrade to newer versions.

root@debian:/opt# ls -l
total 8
drwxr-xr-x 9 root root [...] apache-tomcat-6.0.35
lrwxrwxrwx 1 root root [...] java7 -> jdk1.7.0_03
drwxr-xr-x 8 root root [...] jdk1.7.0_03
lrwxrwxrwx 1 root root [...] tomcat6 -> apache-tomcat-6.0.35

Add a new user for Jenkins and create the base skeleton of Tomcat directories in its homedir /home/jenkins. Copy the conf directory from your Tomcat installation. The other directories are empty. Download the Jenkins WAR file and save it in the webapps directory.

root@debian:/home/jenkins# ls -l
total 28
drwxr-xr-x 2 jenkins nogroup [...] conf
drwxr-xr-x 6 jenkins nogroup [...] data
drwxr-xr-x 2 jenkins nogroup [...] logs
drwxr-xr-x 3 jenkins nogroup [...] temp
drwxr-xr-x 3 jenkins nogroup [...] webapps
drwxr-xr-x 3 jenkins nogroup [...] work

Create /home/jenkins/.profile to define the application server environment variables.

# Applicationserver enviroment
export JENKINS_HOME=/home/jenkins/data
export JENKINS_BASEDIR=${HOME}
export CATALINA_HOME=/opt/tomcat6
export CATALINA_BASE=${HOME}
export JAVA_HOME=/opt/java7
export CATALINA_PID=${JENKINS_BASEDIR}/jenkins.pid
export CATALINA_OPTS="-Xms2048m -Xmx2048m -Djava.awt.headless=true"
export PATH=${CATALINA_HOME}/bin:${JAVA_HOME}/bin:${PATH}

Last step is to put an init script for Jenkins into /etc/init.d/jenkins.

#!/bin/bash
#
# Startup / shutdown script for the jenkins server.
#
### BEGIN INIT INFO
# Provides:             jenkins
# Required-Start:       $network $local_fs
# Required-Stop:
# Should-Start:         $named
# Should-Stop:
# Default-Start:        2 3 4 5
# Default-Stop:         0 1 6
# Short-Description:    Jenkins
# Description:          Jenkins Continuous Integration server
### END INIT INFO

SCRIPT_USER=jenkins
LOCKFILE=/var/lock/jenkins
export TOMCAT_HOME=/opt/tomcat6
[ -f $TOMCAT_HOME/bin/catalina.sh ] || exit 0
case "$1" in
  start)
        # Start daemon.
        echo -n "Starting Jenkins: "
        su -l $SCRIPT_USER -c "$TOMCAT_HOME/bin/catalina.sh start"
        RETVAL=$?
        echo
        [ $RETVAL = 0 ] && touch $LOCKFILE
        ;;
  stop)
        # Stop daemons.
        echo -n "Shutting down Jenkins: "
        su -l $SCRIPT_USER -c "$TOMCAT_HOME/bin/catalina.sh stop"
        RETVAL=$?
        echo
        [ $RETVAL = 0 ] && rm -f $LOCKFILE
        ;;
  restart)
        $0 stop
        $0 start
        ;;
  condrestart)
       [ -e $LOCKFILE ] && $0 restart
       ;;
  status)
        status jenkins
        ;;
  *)
        echo "Usage: $0 {start|stop|restart|status}"
        exit 1
esac
exit 0

Now you can start Jenkins as a seperate service. Repeat the steps from above for each webapp that you need.

This setup makes it possible to start or stop each webapp independent from the others. It also allows you to run webapps with different Java or Tomcat versions or easily change the underlying Java and Tomcat versions (just refer to them in .profile).