Nginx double requests for my upstreams?

[Maxim Dounin]

Hello!

On Tue, Jun 23, 2009 at 10:33:05AM -0400, funkdoobiest wrote:

> Maxim Dounin Wrote:
> -------------------------------------------------------
> > Hello!
> > 
> > On Mon, Jun 22, 2009 at 10:19:54PM -0400,
> > funkdoobiest wrote:
> > 
> > > Hi Maxim,
> > > 
> > > I have checked the nginx-access logs and I found
> > following:
> > > 
> > > 84.72.240.XXX - - [03/Jun/2009:16:38:46 +0200]
> > "POST /premium/paypremium HTTP/1.1" 499 0
> > "http://www.host.com/premium/getpremium/"
> > "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT
> > 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"
> > > 84.72.240.XXX - - [03/Jun/2009:16:38:48 +0200]
> > "POST /premium/paypremium HTTP/1.1" 200 2230
> > "http://www.host.com/premium/getpremium/"
> > "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT
> > 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"
> > > 
> > > 
> > > 
> > > What can I do or what do I wrong?
> > 
> > Error code 499 means that *client* closed
> > connection before it got 
> > response.  In this particular case it looks like
> > duplicate form 
> > submit, e.g. due to second click on submit
> > button.
> > 
> > Maxim Dounin
> 
> I got this 499 error code for about 10% of all the connections. not just for form-submits.

In general 499 errors are normal, since clients tend to close 
browser windows/tabs, cancel downloads or just navigate to another 
page e.g. before loading all images etc.  High percentage of this 
errors may indicate that your site is too slow, but since actual 
numbers depend heavily on site usage pattern it's hard to say what 
is "high".

> It seems that "proxy_ignore_client_abort on;" fix that problem. But why? Is it ok to ignore client aborts?

Directive proxy_ignore_client_abort instructs nginx to finish 
request processing even if client closed connection.  It's safe 
but usually it's just waste of resources (since backend response 
will be thrown away).

Maxim Dounin