Christopher Schultz wrote:
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Bruce,
On 3/5/14, 1:11 PM, Bruce Weertman wrote:
We have a load balancer talking with tomcat’s running on multiple
backend tomcat servers. The tomcats are running web service
applications. In doing testing, and as reported by customers, we
occasionally see refused connections. Not real often, but enough
to be a head ache.
We’re not sure where the problem is coming from. Suspects include
(1) firewall, (2) load balancer (3) tomcat and perhaps the (4) the
web app. The volume of traffic is so high, that it becomes a
needle in a hay stack issue.
Can you describe your setup in a bit more detail? What kind of lb? How
many of them? Any fronting web server(s)? How many? How many Tomcat
instances?
On which platform ? (OS)
What is/are your <Connector> configuration(s)?
We are using the BIO connector and everything is HTTP. Our typical
hit rates are dozens per second.
Tomcat can certainly handle that kind of thing. If you have long
wait-times for your webapp, you might not be able to keep up.
In my experimentation with Tomcat, if it runs out of threads and
the accept queue fills, there is no indication in (for example)
catalina.out.> (see acceptCount and maxConnections in
http://tomcat.apache.org/tomcat-7.0-doc/config/http.html)
Tomcat usually complains if you run out of threads.
In production maxConnections is the default of 200, but when
looking at the number of connections being processed by tomcat it’s
rarely more than a couple dozen per instance. There’s always the
possibility that it occasionally spikes.
What is the resolution of the data you have? Are you sampling with
some regularity?
Anyway, the question is: Is there any good way to see if tomcat
is going into a state where it’s not accepting connections? How
would would I see this? Is it possible to see this ?
Sure: connect to a specific Tomcat. If you get a "connection refused",
then you are in this state.
Your load balancer should have a setting where you can choose a
back-end server explicitly if you want to go through the lb, or you
can just contact one directly.
- -chris
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