Guidance needed - how to track nginx-docker-rails performance issue

Question

My Rails application is deployed on Amazon elastic beanstalk using Docker. Web requests flow into an nginx web server that forwards them to the thin rails server residing in docker. Somewhere along the way there's a bottleneck. Once every 50 requests (or so) I see nginx reports serving time which is x40 higher than the time the rails thin server reports.

here's an example:

NGINX (7490ms):

146.185.56.206 - silo [18/Mar/2015:13:35:55 +0000] "GET /needs/117.json?iPhone HTTP/1.1" 200 2114 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.115 Safari/537.36" 7.490 7.490 .

THIN (rails server): 171ms

2015-03-18 13:35:48.349 [INFO] method=GET path=/needs/117.json format=json controller=needs action=show status=200 duration=171.96 view=109.73 db=29.20 time=2015-03-18 13:35:47

Can anyone supply some guidance how to troubleshoot such a situation? How do I find the source of the response time difference? I guess it could be either nginx or docker or thin or linux.

Gonfva · Accepted Answer · 2015-03-18 17:37:57Z

0

It sounds like one of the thin processes is under load doing a heavy task and nginx is still sending requests to the busy one. If there were a problem of queuing in Thin, the request would take a short time to be processed itself, but longer to get to the top of the queue. So first, check others requests before or around that request.

Second, if you are using upstream to serve (http://nginx.org/en/docs/http/ngx_http_upstream_module.html), apparently you could get among others $upstream_response_time and try to log it.

Third, you could also try to reproduce a similar setup in dev/qa and try a stress test. If you manage to reproduce it consistently, you could see number of request on each queue (i.e. http://comments.gmane.org/gmane.comp.lang.ruby.unicorn.general/848).

answered Mar 18, 2015 at 17:37

Gonfva

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