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From Chris Shenton <Chris.Shen...@hq.nasa.gov>
Subject Bug? Jmeter only tries one addr in multi-addr DNS round robin cluster
Date Wed, 10 Nov 2004 21:41:06 GMT
I'm a jmeter newbie but looked through the docs, FAQ, and mail
archives.  Running jmeter on FreeBSD-4.10 with jdk-1.4.2.  

My target is a set of three app server boxes running Tomcat-4.1.  I've
implemented a cluster with Filip Hanik's back-port of the TC5
clustering code.

  http://cvs.apache.org/%7Efhanik/

I'm trying to test this and make sure it works for us on TC4.

It seems to work fine in simple browser tests.  I have a DNS name
"cluster" which has three A records, one for each node's address.

  cshenton@Palimpsest(347> dnsip cluster.saic.hq.nasa.gov
  198.116.138.39 198.116.138.106 198.116.138.56 

I point Mozilla at this and login, click around, etc -- it returns to
the same node each time.  I disable tomcat on that node.  Upon
subsequent clicks, Mozilla goes to one of the other addresses
associated with the cluster's DNS name.  So this works fine.

But when I configure Jmeter with the same DNS name, it appears that it
looks up the name at startup, only saves one of the three addresses,
and never tries the others.  When re-running the same test, it never
goes to a different host.  If I disable tomcat on the node it's
probing during a run, it continues to try to connect to the dead node
and never goes to another node.  It only goes to a different node if I
actually stop then restart jmeter.

This makes it impossible for jmeter to test DNS round robin based
clusters.  (In my final deployment I'll have a HW load balancer, but
don't have one in my development environment.)

I think Jmeter should be smart enough to cycle through addresses, or
have each thread randomly pick an address from the list DNS provides,
or prefer one and switch to another if the preferred one is
unavailable (TCP Connection Refused is a pretty good sign of that!).

Am I missing something? Is this expected behavior? Desired behavior?

Thanks.


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