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From André Warnier ...@ice-sa.com>
Subject Re: Trouble shooting refused connections
Date Thu, 06 Mar 2014 07:59:20 GMT
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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