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From Paul Leclerc <>
Subject Re: Bug? Jmeter only tries one addr in multi-addr DNS round robin cluster
Date Wed, 10 Nov 2004 23:38:53 GMT
  Don't forget that by default, Java caches IP addresses for DNS
lookups.  See this link for more information: and look
at both networkaddress.cache.ttl  and

On Wed, 10 Nov 2004 16:41:06 -0500, Chris Shenton
<> wrote:
> 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.
> 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
> 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!).

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