Nginx upstream delays

Tue Mar 10 16:59:29 UTC 2015

Does the time reported by Gunicorn match the upstream time reported by
nginx for the faulty request?
- If yes, then the slowdown comes from Gunicorn (or most probably from the
application within)
- If no, then the shallow waters between front and backend needs inspection
by whatever means available, system wide since you are using file
descriptors and inodes from the filesystem with the UNIX sockets

I suggest you monitor the whole machine, which includes the whole OS and
what other processes do, and the whole impact on resources. You will need
to add what happens elsewhere on the machine if you are using a shared
virtualized environment.
Sometimes stuff appearing to be loosely coupled interfere with each other.
:o)

Once again, to me, the trouble definitely does not come from nginx.
---
*B. R.*

On Tue, Mar 10, 2015 at 3:55 PM, Wiebe Cazemier <wiebe at halfgaar.net> wrote:

> Hello,
>
> The definition of the gunicorn time I mentioned is 'request time in
> microseconds'. Because Gunicorn only talks to Nginx, this would be the time
> Gunicorn needs (after having received the request) to generate the response
> and send it back to nginx, I would say. In most cases, this time matches
> the nginx upstream response time closely. There is a few milliseconds
> overhead, usually.
>
> I haven't tried a tcpdump. This is going to require some time to setup,
> because the long delay time is not reproducible. I need to log a day's
> worth of data and then devise some useful filter. I'll try to set something
> up.
>
> As for Maxim's response about packet loss; it would have to be packet loss
> on a file socket. Is this even possible?
>
> - Wiebe
>
>
> ------------------------------
>
> *From: *"B.R." <reallfqq-nginx at yahoo.fr>
> *To: *"nginx ML" <nginx at nginx.org>
> *Sent: *Tuesday, 10 March, 2015 1:28:03 PM
>
> *Subject: *Re: Nginx upstream delays
>
> Then it means nginx waited 3.042 seconds after having finished sending the
> request to the backend (ie time waiting for an answer).
>
> http://nginx.org/en/docs/http/ngx_http_upstream_module.html#var_upstream_response_time
>
> Try to get the definition of the time you mention from Gunicorn. Times
> could be completely different from what you think they mean.
>
> Have you tried to use tcpdump on the frontend/backend communication? Does
> it show anything interesting?
> If the latency comes from neither ends specifically but from the
> communication channel itself, you will need to dig further.
> If it comes fro mthe backend, it might also be some waiting time
> (database? buffering?), which might not taken into account in the time you
> mentioned.
>
> The only certainty is: nginx is responsible for an overhead of 56ms on
> this request. Definitely not a problem on its side, I would conclude.
> ---
> *B. R.*
>
> On Tue, Mar 10, 2015 at 10:23 AM, Wiebe Cazemier <wiebe at halfgaar.net>
> wrote:
>
>> Hello,
>>
>> The $request_time and $upstream_request_time are already included. In
>> the log below it says '3.042 3.098'. The latter is the request time, the
>> former the upstream request time. It doesn't seem to be an issue of slow
>> clients (also not for other log entries, they're similar).
>>
>> It's going to be hard to diagnose if Gunicorn says the request takes 40
>> ms, but Nginx says it takes 3042 ms.
>>
>> Hunting on...
>>
>> - Wiebe
>>
>>
>> ------------------------------
>>
>> *From: *"Wandenberg Peixoto" <wandenberg at gmail.com>
>> *To: *nginx at nginx.org
>> *Sent: *Tuesday, 10 March, 2015 1:37:09 AM
>> *Subject: *Re: Nginx upstream delays
>>
>>
>> You also have to consider the rate your client get data from the server.
>> The request time is the entire time spent from the beginning of the
>> request until the end of response.
>> So you may not have a problem on your server, just a lazy client :)
>>
>> On Mon, Mar 9, 2015 at 1:05 PM, B.R. <reallfqq-nginx at yahoo.fr> wrote:
>>
>>> 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
>>>>
>>>>
>>>>
>>
> _______________________________________________
> nginx mailing list
> nginx at nginx.org
> http://mailman.nginx.org/mailman/listinfo/nginx
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.nginx.org/pipermail/nginx/attachments/20150310/49da740b/attachment-0001.html>