load balancing questions

[Kelly Kleinfelder <ke...@unboundmedicine.com>]

Is there an lbfactor setting that will redirect all new sessions to another worker? 
Is there an upper limit to which the lbfactor can be set? 

With those questions in mind, here is more detail and background for my situation.
 
Here is our setup:

Apache 1.3.14
Tomcat 3.2.1
Solaris 7

We have 2 instances of tomcat running on our web server, tomcat1 and tomcat2. Currently, tomcat1 is used to serve our "live" applications and tomcat2 serves as a testing ground before the apps go live. Our apache server, through the httpd.conf file, includes our tomcat1 configuration file for the "live" apps.
 
Currently, when we move the apps from the testing ground to be the "live" apps, we have to wait until there are no users logged in, and then do the switch, in order to ensure that no user will be kicked out in the middle of his session. What we actually do to initiate the switchover is change the Include line in apache's httpd.conf file to load the configuration file for our testing tomcat, tomcat2, and restart apache. At that point, the testing grounds become the "live" app and the former "live" app tomcat, tomcat1, is used for our new testing ground.

We want to use the load balancing features of tomcat so that we can perform the switchover without disrupting any user sessions. We propose to set the lbfactor of the testing tomcat, tomcat2, to 99 and the "live" server, tomcat1, to 1 when we're ready to switch. That way, any users who have current sessions will continue to visit the former "live" tomcat, tomcat1, and any new user sessions established will be handled by the former testing tomcat, tomcat2. 

We have tested this workers.properties configuration, and while it does send a greater number of new sessions to tomcat2, we still get some that go to tomcat1. Also, when we set the lbfactor for tomcat2 to be 0, it still kicks in and takes over when we stop tomcat1 (even though the documentation says that the lbfactor must be greater than 0). 

Kelly Kleinfelder
UNIX System Administrator
Unbound Medicine, Inc.
610-627-9090 x229