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
 

Load Balancing tomcat with Apache and mod jk

Tomcat works fairly under heavy loads. But many a times we would like to distribute the requests to more than one server to minimize response time and there by improving the user experience. This tutorial shows how to configure load balancing (distribute the load) between two tomcat instances in the same system (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 and also know how to connect apache with tomcat using mod_jk.

All we will do here is to add a new worker to the worker.properties file we already saw in the previous tutorials with Apache httpd 2.x, tomcat 6.x and tomcat-connector 1.2.27.

Below is the content of 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 = loadbalancer   

# ------------------------
# First worker
# ------------------------
worker.tomcat1.port=8009      # Give the ajp port of the first tomcat instance here
worker.tomcat1.host=localhost # You can mention any other hostname or IP here
worker.tomcat1.type=ajp13
worker.tomcat1.lbfactor=100    
worker.tomcat1.connection_pool_timeout=600
worker.tomcat1.socket_timeout=600
worker.tomcat1.recovery_options=16

# ------------------------
# Second worker
# ------------------------
worker.tomcat2.port=9009      # Give the ajp port of the first tomcat instance here
worker.tomcat2.host=localhost # You can mention any other hostname or IP here
worker.tomcat2.type=ajp13
worker.tomcat2.lbfactor=100
worker.tomcat2.connection_pool_timeout=600
worker.tomcat2.socket_timeout=600
worker.tomcat2.recovery_options=16

# ------------------------
# Load Balancer 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.loadbalancer.type=lb
worker.loadbalancer.balance_workers=tomcat1, tomcat2
worker.loadbalancer.sticky_session=False
worker.loadbalancer.sticky_session_force=False

# END workers.properties
 

Note: You can have as many tomcat instances(workers) as you want in the same box as long as your box can withstand the load.