wrong values for $upstream_response_time in add_header?

[Maxim Dounin]

Hello!

On Fri, May 04, 2012 at 10:19:49AM +0200, Christian Bönning wrote:

> I'm cross-posting this from the forums to the mailinglist in hope for
> getting a reply here. Sorry for that.
> 
> I'm using nginx-1.2.0 (plus upstream-fair and headers-more; for
> complete `nginx -V` and `uname -a` please see
> https://gist.github.com/be4a86dbfdae516a4efe) and I'm really happy
> with that. However I want to add a couple of Headers
> ($upstream_response_time in this case) to be passed to the Client for
> debugging purposes. So I've added `add_header X-AppServer-Response
> $upstream_response_time;` to my location block where I do all my proxy
> stuff. I've got an upstream block where I've put in my 3 backend
> servers. All Backends respond very fast during testing.
> 
> However there are unreasonable high values within this header
> (X-AppServer-Response: 74768.562 in this case). I'm using access_log
> to get some more values written to disk as well for central
> monitoring. Within this log all values seem to be ok (for this
> particular request it's 0.002 to be exact).
> 
> I was able to reproduce that behaviour using different backends
> (apache2 and another nginx in this case).
> 
> Any Idea what's going wrong here?

The $upstream_response_time is only meaningful once response is 
fully got from upstream, and this happens after response headers 
are got (and sent to client).  That is, you basically can't use 
$upstream_response_time in add_header, only in logs.

Maxim Dounin