Using memcache to set variables

[Valery Kholodkov]

----- Valery Kholodkov <valery+nginxen at grid.net.ru> wrote:
> 
> ----- Marcus Clyne <maccaday at gmail.com> wrote:
> > Hi,
> > 
> > Avleen Vig wrote:
> > > On Aug 12, 2009, at 6:08, Johan Bergström <johan at bergstroem.nu> wrote:
> > >
> > >> Hey,
> > >> On Aug 8, 2009, at 05:13 , Avleen Vig wrote:
> > >>
> > >>> I started using the geo module to direct users by IP address, this
> > >>> week, and really like it!
> > >>>
> > >>> It got me thinking about another thing I've been wanting to do: Direct
> > >>> users to different machines based on some arbitrary data. I don't want
> > >>> to rely just on cookies, because those can be manipulated. Here's what
> > >>> I was thinking, and I'm wondering if it can be done some how in nginx?
> > >>>
> > >>> The sessionid is stored in a cookie. This can't be manipulated or the
> > >>> users ends up not being logged in.
> > >>> Store the sessionid in memcache, and have the value set to the name of
> > >>> a location.
> > >>> Have nginx fetch the value for 'sessionid' from memcache, and then
> > >>> redirect the user internally to that location.
> > >>>
> > >>> Is this even remotely possible? I think some hardware load balancers
> > >>> can do it, but I'm too poor to buy one of those :-)
> > >>
> > >> We're doing something similar - through a FastCGI-app written in C - 
> > >> which looks up a host as key in memcached (cookie would work just as 
> > >> fine) and returns a backend (we have lots of different nginx 
> > >> backends) that the frontends proxies to. The key here is to use 
> > >> X-Accel-Redirect. So, in short: Yes, it's possible and delivers ~2k 
> > >> r/s per frontend for us. A FastCGI/whatever app written in php/python 
> > >> would probably work just as well, port to C when performance is needed.
> > >
> > > Hi Johan!
> > >
> > > Thus is exactly what I'm hoping to do!
> > > How do you use x-accel-redirect to get the name of a backend? I've 
> > > never used it. Do ou have any code examples? This would be really 
> > > perfect.
> > Have a look at the eval module written by Valery Kholodkov - as mentioned.
> > 
> > A possible setup might be:
> > 
> > eval $location {
> >     set $memcached_key   $cookie_sid;
> >     memcache_pass   name:11211;
> > }
> > 
> > location / {
> >     try_files   $location @fallback;
> > }
> > 
> > 
> > location /_/ {
> >     # add directives here if desired
> >     internal;
> > }
> > 
> > 
> > @fallback {
> >     [directives to generate session ID or location]
> >     fastcgi_pass ...
> > }
> > 
> > 
> > I've not tested this config, though, so I don't guarantee it will work, 
> > but something like it should work I think.  I added the /_/ location to 
> > avoid infinite loops in the location / {} block, though there are many 
> > ways you could achieve the same result ( locations returned from 
> > memcached would have /_/-prefixed URLs).
> 
> For this task X-Accel-Redirect is more suitable.

Ahh sorry, I thought you were still talking about fastcgi. I am wrong. For memcached your approach is still suitable, since memcached cannot return X-Accel-Redirect.

-- 
Regards,
Valery Kholodkov