Introduction
This document will teach us how to setup Tomcat to run
Multiple instances of it.
Intended Audience: System admins.
Instruction to installing Tomcat so that we can run multiple
instances.
1. Install the Tomcat files
Download Tomcat and unzip it into an appropriate directory.
I usually put it in /opt, so it ends up in a directory called
/opt/apache-Tomcat-6.0.29 (6.0.29 being the current version as of this
writing), and make a symlink named /opt/tomcat to that directory. When later
versions come out, we can unzip them and relink, leaving the older version in
case things don’t work out (which rarely if ever happens, but as system admins
we are paranoid).
2. Add user for each instance
For each instance of Tomcat we’re going to run, we’ll need
to add a user and create Tomcat directory in it that will be CATALINA_BASE. For
example, we will add users Tomcat1 and Tomcat2 and create Tomcat directory the
CATALINA_BASE will be /home/Tomcat1/Tomcat and /home/Tomcat2/Tomcat2 respectively.
In each users home directory we need the following sub
directories: conf, logs, temp, webapps, and work.
We will copy these sub directories from /opt/tomcat in the
Tomcat directory of the user. Of course you should tighten up your server.xml a
bit.
The webapps directory is where you’ll put the web
applications you want to run on the particular instance of Tomcat.
We like to have the Tomcat manager webapp installed on each
instance, so we can play with the webapps, and see how many active sessions
there are.
3. Configure the ports and/or addresses for each instance
Tomcat listens to at least three network ports, one for the
shutdown command, one for accepting requests on HTTP and one for accepting
connection on AJP port. Two instances of Tomcat can’t listen to the same port
number on the same IP address, so we will edit our server.xml files to change
the ports they listen to.
The first port to look at is the shutdown port. This is used
by the command line shutdown script (actually, but the Java code it runs) to
tell the Tomcat instance to shut itself down. This port is defined at the top
of the server.xml file for the instance.
1
Make sure each instance uses a different port value. The
port value will normally need to be higher than 1024, and shouldn’t conflict
with any other network service running on the same system. The shutdown string
is the value that is sent to shut the server down. Note that Tomcat won’t
accept shutdown commands that come from other machines.
Unlike the other ports Tomcat listens to, the shutdown port
can’t be configured to listen to its port on a different IP address. It always
listens on 127.0.0.1.
The other ports Tomcat listens to are configured with the
elements, for instance the HTTP or JK listeners. The port
attribute configures which port to listen to. Setting this to a different value
on the different Tomcat instances on a machine will avoid conflict.
Of course, we’ll need to configure whatever connects to that
Connector to use the different port. If a web server is used as the front end
using mod_jk, mod_proxy, or the like, then this is simple enough – change our
web server’s configuration.
In some cases we may not want to do this, for instance you
may not want to use a port other than 8080 for HTTP connectors. If you want all
of your Tomcat intances to use the same port number, you’ll need to use
different IP addresses. The server system must be configured with multiple IP addresses
and the address attribute of the element for each Tomcat
instance will be set to the appropriate IP address.
Ports to be changed listed below:
8005
8080
8009
8443
4. Startup
Startup scripts are a whole other topic, but here’s the
brief rundown. The main different from running a single Tomcat instance is we
need to set CATALINA_BASE to the directory you set up for the particular
instance you want to start (or stop).
Put the following in users .bash_profile or .bashrc:
1.
JAVA_OPTS="-Xmx800m -Xms800m"
2.
CATALINA_HOME=/opt/tomcat
3.
CATALINA_BASE=~/tomcat
4.
export JAVA_HOME JAVA_OPTS CATALINA_HOME
CATALINA_BASE
Save and close the file. Start the Tomcat with following
command
$CATALINA_HOME/bin/catalina.sh start
That’s it now we can run multiple instances of Tomcat
without making the redundant copies of Tomcat binaries and libraries.
