Nginx upstream delays

Mon Mar 9 16:05:04 UTC 2015

You are on a nginx mailing list, thus I will reply on the nginx side of the
problem.

You can diagnose further to tell if the problem comes from nginx or from
the backend by using 2 different variables in your log message:
$request_time
<http://nginx.org/en/docs/http/ngx_http_log_module.html#var_request_time>
$upstream_response_time
<http://nginx.org/en/docs/http/ngx_http_upstream_module.html#var_upstream_response_time>

If those values are close enough (most of the time equal), you might then
conclude that the trouble does not come from nginx, but rather from the
backend (or communication between those).

If you want to investigate the communication level, you can set up some
tcpdump listening on the communication between nginx and the backend. You
will need to use TCP ports to do that.
Since you are using UNIX sockets, you might want to monitor file
descriptors, but I would (totally out of thin air) suppose it might not be
the source of your trouble, since you would have seen much more impact if
it was.

I guess you will have to trace/dump stuff on your backend. PHP has some
slowlog capability firing up tracing in a code which takes too long to
finish. I do not know anything about Python servers, but you are not at the
right location for questions related to those anyway.

Happy hunting,
---
*B. R.*

On Mon, Mar 9, 2015 at 4:28 PM, Wiebe Cazemier <wiebe at halfgaar.net> wrote:

> Hello,
>
> 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):
>
> 11.22.33.44 - - [06/Mar/2015:10:27:46 +0100] "GET /customer/login/
> HTTP/1.1" 200 8310 0.061 0.121 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:48 +0100] "GET /customer/login/
> HTTP/1.1" 200 8310 0.035 0.092 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:52 +0100] "GET /customer/login/
> HTTP/1.1" 200 8310 3.042 3.098 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:53 +0100] "GET /customer/login/
> HTTP/1.1" 200 8310 0.051 0.108 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:54 +0100] "GET /customer/login/
> HTTP/1.1" 200 8310 0.038 0.096 "-" "Echoping/6.0.2"
> x.x.x.x         - - [06/Mar/2015:10:27:58 +0100] "POST
> /customer/login/?next=/customer/home/ HTTP/1.1" 302 5 0.123 0.123
>
>
> But then the corresponding Gunicorn logs shows normal response times (the
> figure after 'None', in µs) (Corresponding line marked blue):
>
>
> 11.22.33.44 - - [06/Mar/2015:10:27:41] "GET /customer/login/ HTTP/1.0" 200
> None 41686 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:42] "GET /customer/login/ HTTP/1.0" 200
> None 27629 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:43] "GET /customer/login/ HTTP/1.0" 200
> None 28143 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:44] "GET /customer/login/ HTTP/1.0" 200
> None 41846 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:45] "GET /customer/login/ HTTP/1.0" 200
> None 30192 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:46] "GET /customer/login/ HTTP/1.0" 200
> None 59382 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:48] "GET /customer/login/ HTTP/1.0" 200
> None 33308 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:52] "GET /customer/login/ HTTP/1.0"
> 200 None 39849 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:53] "GET /customer/login/ HTTP/1.0" 200
> None 48321 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:27:54] "GET /customer/login/ HTTP/1.0" 200
> None 36484 "-" "Echoping/6.0.2"
> x.x.x.x     - - [06/Mar/2015:10:27:58] "POST
> /customer/login/?next=/customer/home/ HTTP/1.0" 302 None 122295
> y.y.y.y     - - [06/Mar/2015:10:28:02] "GET
> /customer/login/?next=/customer/home/ HTTP/1.0" 200 None 97824
> y.y.y.y     - - [06/Mar/2015:10:28:03] "GET
> /customer/login/?next=/customer/home/ HTTP/1.0" 200 None 78162
> 11.22.33.44 - - [06/Mar/2015:10:28:26] "GET /customer/login/ HTTP/1.0" 200
> None 38350 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:28:27] "GET /customer/login/ HTTP/1.0" 200
> None 31076 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:28:28] "GET /customer/login/ HTTP/1.0" 200
> None 28536 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:28:30] "GET /customer/login/ HTTP/1.0" 200
> None 30981 "-" "Echoping/6.0.2"
> 11.22.33.44 - - [06/Mar/2015:10:28:31] "GET /customer/login/ HTTP/1.0" 200
> None 29920 "-" "Echoping/6.0.2"
>
>
> As I said, there are currently 8 workers. I already increased them from 4.
> The log above shows that there are enough seconds between each request that
> 8 workers should be able to handle it. I also created a MySQL slow log,
> which doesn't show the delays. MySQL is always fast.
>
> Another server we have is Nginx with PHP-FPM (with 150 PHP children in the
> pool), no database access. On one particular recent log of a few hundred
> thousand entries, 99% of requests is done in 129ms. But one response even
> took 3170ms. Its PHP proxy settings are:
>
> location ~ \.php$ {
>   fastcgi_split_path_info ^(.+\.php)(/.+)$;
>   # NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini
>
>   # With php5-fpm:
>   fastcgi_pass unix:/var/run/php5-fpm.sock;
>   fastcgi_index index.php;
>   include fastcgi_params;
> }
>
>
> It seems something in the communication between Nginx and the service
> behind it slows down sometimes, but I can't figure out what it might be.
> Any idea what it might be or how to diagnose it better?
>
> Regards,
>
> Wiebe Cazemier
>
>
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>
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