Socket connection failures on 1.6.1~precise

Jon Clayton jon.clayton at
Tue Sep 2 20:35:03 UTC 2014

I did see the changelog hadn't noted many changes and running a diff of 
the versions shows what you mentioned regarding the 400 bad request 
handling code.  I'm not necessarily stating that nginx is the problem, 
but it would seem like something had changed enough to cause the 
backend's backlog to fill more rapidly.

That could be a completely bogus statement as I've been attempting to 
find a way to track down exactly what backlog is being filled, but my 
test of downgrading nginx back to 1.6.0 from the nginx ppa seemed to 
also point at a change in nginx causing the issue since the errors did 
not persist after downgrading.

It's very possible that I'm barking up the wrong tree, but the fact that 
only changing nginx versions back down to 1.6.0 from 1.6.1 eliminated 
the errors seems suspicious.  I'll keep digging, but I'm open to any 
other suggestions.

On 09/02/2014 02:14 PM, Maxim Dounin wrote:
> Hello!
> On Tue, Sep 02, 2014 at 11:00:10AM -0500, Jon Clayton wrote:
>> I'm trying to track down an issue that is being presented only when I run
>> nginx version 1.6.1-1~precise.  My nodes running 1.6.0-1~precise do not
>> display this issue, but freshly created servers are getting floods of these
>> socket connection issues a couple times a day.
>> /connect() to unix:/tmp/unicorn.sock failed (11: Resource temporarily
>> unavailable) while connecting to upstream/
>> The setup I'm working with is nginx proxying requests to a unicorn socket
>> powered by a ruby app.  As stated above, the error is NOT present on nodes
>> running 1.6.0-1~precise, but any newly created node gets the newer
>> 1.6.1-1~precise package installed and will inevitably have that error.
>> All settings from nodes running 1.6.0 appear to be the same as newly created
>> nodes on 1.6.1 in terms of sysctl settings, nginx settings, and unicorn
>> settings.  All package versions are the same except for nginx.  When I
>> downgraded one of the newly created nodes to nginx 1.6.0 using the nginx ppa
>> (ref:
>>, the error was not
>> present.
>> Is there any advice, direction, or similar issue experienced that someone
>> else might be able to help me track this down?
> Just some information:
> - In nginx itself, the difference between 1.6.0 and 1.6.1 is fairy
>    minimal.  The only change affecting http is one code line added
>    in the 400 Bad Request handling code
>    (see
> - The message suggests that backend's backlog is full.  This can
>    easily happen on load spikes and/or if a backend is overloaded,
>    and usually unrelated to the nginx itself.

More information about the nginx mailing list