How to set up multiple Tomcat instances?

Have you considered configuring several webapps directories instead of running multiple tomcat instances?

Of course there are cases where you really need multiple instances but in case of serving same application separately for multiple hosts, you may do it by adding multiple declarations in server.xml:

  <Host name="host1.example.com" appBase="host1"
    unpackWARs="true" autoDeploy="true" 
    xmlValidation="false" xmlNamespaceAware="false" />

  <Host name="host2.example.com" appBase="host2"
    unpackWARs="true" autoDeploy="true" 
    xmlValidation="false" xmlNamespaceAware="false" />

Now you may create "/var/lib/tomcat6/host1" and "/var/lib/tomcat6/host2" directories and deploy WAR files to them.

I am setting this up on Ubuntu 14.04.3 LTS. I am using the Tomcat 7 provided by the tomcat7 package.

It installs Tomcat as a system service by providing a standard init script:

/etc/init.d/tomcat7

and configuration file:

/etc/default/tomcat7

Tomcat supports running multiple instances with the same server software. The server software is located in $CATALINA_HOME, the files for the instance are located in $CATALINA_BASE. They are defined as follows in /etc/init.d/tomcat7:

NAME=tomcat7
CATALINA_HOME=/usr/share/$NAME
CATALINA_BASE=/var/lib/$NAME

(Caveat: when editing files in the latter, be aware that it has some symlinks into the former.)

The tomcat7-user package provides the utility tomcat7-instance-create that can be used to create a directory tree for an additional Tomcat instance, including a bin/ directory with scripts for starting and stopping the instance manually.

What I haven't found is support for turning such an additional instance into a system service. Therefore, it must be done manually, e.g. as follows:

1. Pick a value for the service name; it will be $NAME in the new init script.
2. Create a new user with that name that will own the files for the Tomcat instance and as which Tomcat will run. It can be a system user, its properties should be the same as for the tomcat7 user.
3. Run tomcat7-instance-create as that user to create a Tomcat instance.
4. Configure it and install the web application(s) you want to run with it. Test them using its bin/startup.sh and bin/shutdown.sh scripts.
5. Move the logs to /var/log/$NAME and symlink them back to logs/ of the new Tomcat instance.
6. Write /etc/init.d/$NAME, e.g. by copying and modifying /etc/init.d/tomcat7 and modifying the assignment to $NAME. (It would be nicer if you didn't need to copy the whole script but could just create a link to it.)
7. Write /etc/default/$NAME to point at your Tomcat instance and user.
8. Use upstart-rc.d to install the new service.

I gleaned some of the details from Kodjo-Kuma Djomeda.