# 2048 worker\_connections are not enough while connecting to upstream

**URL:** <https://www.ruby-forum.com/t/2048-worker-connections-are-not-enough-while-connecting-to-upstream/206791>\
**Category:** NGINX\
**Created:** [May 10, 2011, 11:28am UTC](https://www.ruby-forum.com/t/2048-worker-connections-are-not-enough-while-connecting-to-upstream/206791 "2011-05-10T11:28:41Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\
**Post date:** [May 10, 2011, 11:28am UTC](https://www.ruby-forum.com/t/2048-worker-connections-are-not-enough-while-connecting-to-upstream/206791/1 "2011-05-10T11:28:41Z")

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I’m using nginx as a remote proxy server in front of some Tomcat  
instances, with pretty high traffic. Suddenly yesterday afternoon we  
started getting the error in the message subject, one I’d never seen  
before, and it’s occurred tens of thousands of times since. Now, I’ve  
upped the worker\_connections count to a much higher figure and the  
problem has gone away for now. But I’m concerned that it might be  
indicative of something else - some kind of DOS attack, maybe? What does  
this signify and why might we suddenly start getting it? Thanks.

John

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**Author:** ![jmaenpaa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9de053/32.png) [@jmaenpaa](https://www.ruby-forum.com/u/jmaenpaa)\
**Post date:** [May 10, 2011, 12:20pm UTC](https://www.ruby-forum.com/t/2048-worker-connections-are-not-enough-while-connecting-to-upstream/206791/2 "2011-05-10T12:20:02Z")

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Hello!

On Tue, May 10, 2011 at 10:31:06AM +0100, John M. wrote:

> I’m using nginx as a remote proxy server in front of some Tomcat  
> instances, with pretty high traffic. Suddenly yesterday afternoon we  
> started getting the error in the message subject, one I’d never seen  
> before, and it’s occurred tens of thousands of times since. Now,  
> I’ve upped the worker\_connections count to a much higher figure and  
> the problem has gone away for now. But I’m concerned that it might  
> be indicative of something else - some kind of DOS attack, maybe?  
> What does this signify and why might we suddenly start getting it?  
> Thanks.

Without proper history graphs (use stub\_status, Luke!) it’s hard  
to say if you are under attack or just your normal load reached  
the bar (or your backend response time degraded and this resulted  
in more connections used, or your network uplink has problems and  
this caused more connections…).

On the other hand, 2048 is pretty low, and easily reached even  
without keepalive. Usual production values for “high traffic”  
sites is over 9000.

Please also note that using high worker\_connections may also  
require tuning of your OS to allow appropriate number of file  
descriptors to be used.

Maxim D.

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<div class="post-metadata">

**Author:** ![jmaenpaa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9de053/32.png) [@jmaenpaa](https://www.ruby-forum.com/u/jmaenpaa)\
**Post date:** [May 10, 2011, 12:29pm UTC](https://www.ruby-forum.com/t/2048-worker-connections-are-not-enough-while-connecting-to-upstream/206791/3 "2011-05-10T12:29:57Z")

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On 10/05/11 11:19, Maxim D. wrote:

> > the problem has gone away for now. But I’m concerned that it might  
> > be indicative of something else - some kind of DOS attack, maybe?  
> > What does this signify and why might we suddenly start getting it?  
> > Thanks.
> 
> Without proper history graphs (use stub\_status, Luke!) it’s hard  
> to say if you are under attack or just your normal load reached  
> the bar (or your backend response time degraded and this resulted  
> in more connections used, or your network uplink has problems and  
> this caused more connections…).

I’ll look into these.

> On the other hand, 2048 is pretty low, and easily reached even  
> without keepalive. Usual production values for “high traffic”  
> sites is over 9000.

OK, I may bump it up a bit higher than the 8192 I set it as today.

> Please also note that using high worker\_connections may also  
> require tuning of your OS to allow appropriate number of file  
> descriptors to be used.

I made this change a while back, so we should be OK with that.

Thanks for your extremely lucid help!

John