atom feed5 messages in ru.sysoev.nginxRe: Race condition in limit_zone/limi...
FromSent OnAttachments
Barry JaspanMay 3, 2010 12:37 pm 
Maxim DouninMay 3, 2010 4:58 pm 
Barry JaspanMay 4, 2010 9:09 am 
Maxim DouninMay 4, 2010 10:27 am 
Barry JaspanMay 4, 2010 12:08 pm 
Subject:Re: Race condition in limit_zone/limit_conn?
From:Maxim Dounin (mdou@mdounin.ru)
Date:May 4, 2010 10:27:24 am
List:ru.sysoev.nginx

Hello!

On Tue, May 04, 2010 at 12:10:26PM -0400, Barry Jaspan wrote:

Maxim,

Thank you for your reply.

On Mon, May 3, 2010 at 7:58 PM, Maxim Dounin <mdou@mdounin.ru> wrote:

You had at least 7 connections (*1, *2, *4, *6, *8, *9, *10) during the test. First 3 were passed through, others were rejected. ... Most likely you configured nginx to proxy to itself and this causes extra connections.

I understand how making nginx proxy to itself would cause extra connections and how those might make all of the initial connections fail. If the limit is 3, I open 3, then each of those 3 attempt to proxy to nginx again, nginx will return 503 to the proxy request which will then be returned to the original requests.

However, I do not see how that is happening in my case.

Sure, but 1) you haven't provided any evidence it doesn't happen with 3 requests and 2) even assumming it doesn't happen - nobody says loop is unconditional.

I have reduced my configuration file to a minimum. Here it is:

---- snip snip ---- user nginx; worker_processes 10; error_log /var/log/nginx/error.log debug; pid /var/run/nginx.pid; events { worker_connections 2048; } http { proxy_set_header Host $host; limit_zone max_conn $host 10m; limit_conn max_conn 3; server { listen 80; server_name _; location / { proxy_pass http://10.252.86.98; } } } ---- snip snip ----

Does this config file make nginx proxy to itself? I do not see how.

The question is: what handles connections on 10.252.86.98:80 and how it handles them? In most simple case it's the same nginx, and loop is clear enough.

[...]

Any thoughts?

Your logs clearly show there are more requests than you expect from ab. And your config doesn't make proxy loop impossible.

You may either remove "proxy_set_header Host $host" to make sure Host header in original request will differ from one in proxied, or add something like

proxy_set_header X-Loop-Test washere;

to make sure requests will be at least distingushable in debug log.

Maxim Dounin

_______________________________________________ nginx mailing list ngi@nginx.org http://nginx.org/mailman/listinfo/nginx