I think I noticed this behavior too. The upstream didn't fail but it
tried multiple in parallel anyway.

On Jun 7, 2009, at 12:35 PM, "funkdoobiest" <nginx-forum@nginx.us>
wrote:

> Hi Maxim,
>
> Maxim Dounin Wrote:
> -------------------------------------------------------
>> Hello!
>>
>> On Fri, Jun 05, 2009 at 07:59:13AM -0400,
>> funkdoobiest wrote:
>>
>>> Hi,
>>>
>>> I have a strange behavior for my site load
>> balanced with nginx.
>>> I have 1 Loadbalancer with nginx and 3 servers
>> with apache.
>>>
>>> sometimes a request is doubled and send to 2 of
>> my apache webservers.
>>> this is a big problem for me, because this is
>> sometimes a requests that is doing a payement.
>>> I checked this behavior with doing a log of all
>> my payment transactions and there a some
>> transactions
>>> for the same person double at the same second!
>> (the user can't do this at the website, because I
>> send the form which is doing the request with JS
>> and ask the User if he really wants to pay and so
>> on)
>>
>> http://wiki.nginx.org/NginxHttpProxyModule#proxy_n
>> ext_upstream
>>
>> Maxim Dounin
>
> Thank you for your help. I set proxy_next_upstream to off, but there
> are still double requests :-(
>
> Posted at Nginx Forum: http://forum.nginx.org/read.php?2,2644,2689#msg-2689
>
>