[twill] Monitoring Web Applications Behind Load Balancer?

Mart Doyle mdoyle at temple.edu
Mon Nov 1 12:19:56 PDT 2010

We're been exploring the use of twill to help us monitor web based
applications and have been making good progress.  We're run into one problem
which I thought I would bounce off of this group to see if there were any
"best practices" for dealing with this type of issue.


We have a small group of our most important applications sitting behind a
load balancer.  For example, we have a collection of web servers which all
support an application  called Blackboard.  If I have three of these
Blackboard servers sitting behind the load balancer, I can create three
twill scripts which monitor the application on each of these web servers.
However, I really don't care if one or even two of these web servers are
down.  As long as one of these web servers is functioning, the application
is considered to be "up".


I'd really just like to go to one URL, let the load balancer direct me to
one of the available application servers, and test to verify that the
application server is responding to a scripted login request.
Unfortunately, our twill scripts don't seem to be being redirected to the
respective application servers so we've been forced to run multiple scripts,
one for each application server, and need to determine if all three
application servers are not responding before we flag the application as


How do we do this?  I'd like to be able to test all three, set some type of
"condition code" for each test, and then only return a failure if all three
condition codes indicate a failure but it doesn't appear as if twill has the
ability to compare values, branch, etc.  


Any suggestions?



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