Nginx upstream delays

[Maxim Dounin]

Hello!

On Mon, Mar 09, 2015 at 04:28:22PM +0100, Wiebe Cazemier wrote:

> I have a question about sporadic long upstream response times 
> I'm seeing on (two of) our Nginx servers. It's kind of hard to 
> show and quantify, but I'll do my best. 
> 
> One is a Django Gunicorn server. We included the upstream 
> response time in the Nginx access log and wrote a script to 
> analyze them. What we see, is that on the login page of a 
> website (a page that does almost nothing) 95%-99% of 'GET 
> /customer/login/' requests are processed within about 50 ms. The 
> other few percent can take several seconds. Sometimes even 5s. 
> Our Munin graphs show no correlation in disk latency, cpu time, 
> memory use, etc. 
> 
> I also added an access log to Gunicorn, so that I can see how 
> long Gunicorn takes to process requests that Nginx thinks take 
> long. Gunicorn has 8 workers. It can be seen that there is 
> actually no delay in Gunicorn. For instance, Nginx sees this 
> (the long upstream response time is marked red, 3.042s): 

The 3s time suggests there is a packetloss somewhere.

-- 
Maxim Dounin
http://nginx.org/