Tomcat Failover Setup with Apache2+modjk

Tomcat works fairly well under heavy loads. For critical services we will need some type of backup/failover mechanism. This tutorial is for those who want to configure apache to failover between two tomcat instances. When the first tomcat service fails, apache-httpd automatically routes the requests to second tomcat.

This tutorial shows how to configure failover load balancing between two tomcat instances in the same server (i have also shown how to do this for tomcat instances in two different servers). For this i am assuming you know how to install multiple tomcat instances in the same machine. This is only slightly different from load balancing between two tomcat instances as you see below in the sample workers.properties file.

#
# workers.properties
#
# Below Entry Specifies the load balance factor when used with a load balancing worker.
# Note: ----> lbfactor must be > 0,  Low lbfactor means less work done by the worker.
# worker.tomcat1.lbfactor=100

# In Unix, we use forward slashes:
ps=/

# list the workers by name

# Workers that are member of lb should not be in the list.
worker.list = failover

# ------------------------
# Tomcat1 Primary 
# ------------------------
worker.tomcat1.port=8009        # You can specify your tomcat instance's ajp port here
worker.tomcat1.host=localhost # Specify any hostname/IP here if tomcat is running in a remote server
worker.tomcat1.type=ajp13
worker.tomcat1.lbfactor=1
worker.tomcat1.connection_pool_timeout=600
worker.tomcat1.socket_timeout=600
worker.tomcat1.redirect=tomcat2

# ------------------------
# Tomcat2 Failover
# ------------------------
worker.tomcat2.port=9009        # You can specify your tomcat instance's ajp port here
worker.tomcat2.host=localhost # Specify any hostname/IP here if tomcat is running in a remote server
worker.tomcat2.type=ajp13
worker.tomcat2.lbfactor=1
worker.tomcat2.connection_pool_timeout=600
worker.tomcat2.socket_timeout=600
worker.tomcat2.activation=disabled # Requests are sent to the disabled worker only if first worker fails

# ------------------------
# Failover worker
# ------------------------
#
# The loadbalancer (type lb) worker performs weighted round-robin
# load balancing with sticky sessions.
# Note:
# ----> If a worker dies, the load balancer will check its state
# once in a while. Until then all work is redirected to peer
# worker.
worker.failover.type=lb
worker.failover.balance_workers=tomcat1,tomcat2
worker.failover.sticky_session=False
worker.failover.sticky_session_force=False

# END workers.properties
 

Apache and Tomcat with modjk using tar

I have already put together a tutorial to connect Apache HTTP with Apache tomcat. In that i had installed httpd with rpm. This tutorial explains the steps to connect apache(http) with tomcat using modjk ;only that this time i am going to explain how to do everything from tar bundles. Here i am not going to explain how to install tomcat. Another tutorial on that is here: http://techsk.blogspot.com/2008/04/installing-tomcat.html.

In the below tutorial i will be installing apache in the default directory (/usr/local/apache2) you can change that location in your server to any other by adding --prefix=<your-install-directory> in the configuration step before calling make. Also i am installing Apache HTTP with SSL support.

When i get some time i will put together the steps for enabling SSL in apache and for using tomcat's SSL keys in Apache.

Here we go:

First download httpd:
# cd /usr/local/src/
# wget http://apache.mirrors.redwire.net/httpd/httpd-2.2.10.tar.gz
# wget http://www.apache.org/dist/httpd/httpd-2.2.10.tar.gz.md5
# md5sum httpd-2.2.10.tar.gz (was equal to the downloaded sum)
# tar zxfv httpd-2.2.10.tar.gz
# cd httpd-2.2.10

Below command will configure (prepare) apache installation with most of the shared modules. Type ./configure --help to see what they are
# ./configure --enable-so --enable-mods-shared=most --enable-ssl    (Hint: --prefix=</path/to/install/directory>)
# make
# make install
# cd /usr/local/src/
# wget http://www.trieuvan.com/apache/tomcat/tomcat-connectors/jk/source/jk-1.2.27/tomcat-connectors-1.2.27-src.tar.gz
# wget http://www.apache.org/dist/tomcat/tomcat-connectors/jk/source/jk-1.2.27/tomcat-connectors-1.2.27-src.tar.gz.md5
# md5sum tomcat-connectors-1.2.27-src.tar.gz (was equal to the downloaded sum).
# tar zxfv tomcat-connectors-1.2.27-src.tar.gz
# cd tomcat-connectors-1.2.27-src/native/
#  ./configure --with-apxs=/usr/local/apache2/bin/apxs
# make
# make install

That is it for the installation. Now we will configure apache for connecting it with tomcat
# cd /usr/local/apache2/conf/
# cp httpd.conf httpd.conf_18Nov08
# vi httpd.conf
Add the following code below the LoadModule section.

# Load mod_jk
# 
LoadModule jk_module modules/mod_jk.so

# Configure mod_jk
#
JkWorkersFile conf/workers.properties
JkLogFile logs/mod_jk.log
JkLogLevel info

JkMount *.jsp test   <- This must be the worker name you give in workers.properties. This will at(many) times go into your Virtual Host configuration.

Uncomment the line: Include conf/extra/httpd-ssl.conf
Save and Exit.
# cd /usr/local/apache2/conf/
# vi workers.properties (create new file and paste the below code)

# workers.properties
#

# In Unix, we use forward slashes:
ps=/

# list the workers by name

worker.list=test

# ------------------------
# First tomcat server
# ------------------------
worker.test.port=8009
worker.test.host=localhost
worker.test.type=ajp13

#
# END workers.properties
#

Save and exit.

Start Apache.
# /usr/local/apache2/bin/apachectl start

Now you will be able to browse all jsp pages through apache. Apache will silently be connecting with tomcat through modjk to serve those.

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