Nginx gets halt on 15K connections !!

[Valentin V. Bartenev]

On Thursday 07 May 2015 18:38:23 shahzaib shahzaib wrote:
> Hi,
> 
>   It looks like we made the false calculation based on entertaining
> concurrent connections per seconds and worker_connections limit was set to
> be very low. I've increased this limit to 16000 and issue looks to be
> fixed. Here's the mechanism i used to calculate concurrent connections/sec:
> 
>  worker_processes * worker_connections / keepalive_timeout == concurrent
> connections per second
> 
> Concurrent connections on our server is around 15K . Based on this i used
> the following values :
> 
>  48 * 16000 / 15 == 51200/sec
> 
> Can somebody point to me if the calculation method is false ?
> 
[..]

It's false.

The keepalive_timeout has nothing to do with the concurrent connections per second.
In fact, nginx can close an idle connection at any time when it reaches the limit
of worker_connections.

What's really important is the connections that nginx cannot close.  The active ones.
How long the connection is active depends on the request processing time.

The approximate calculation looks like this:

 worker_processes * worker_connections * K / average $request_time

where K is the average number of connections per request (for example, if you do proxy
pass, then nginx needs additional connection to your backend).

  wbr, Valentin V. Bartenev