New nginx module: ngx_softlimit

[scyth]

On Wed, 30 Jun 2010 20:53:58 +0400
Maxim Dounin <mdounin at mdounin.ru> wrote:

> Hello!
> 
> On Wed, Jun 30, 2010 at 06:28:51PM +0200, Zeljko Tomic wrote:
> 
> > I wrote a small, but sometimes very useful module for limiting 
> > the number of active connections, in a "soft" way.
> > 
> > Description and usage:
> > -----------------------
> > In situation when using nginx for serving static files and 
> > primarily as a proxy/proxy_cache with some slower backend (or 
> > even php fastcgi), limits of connections and requests that nginx 
> > can handle are much higher than they are on backend server(s). 
> > When you know the limits of your backend, it is bad practice to 
> > apply those limits on nginx's worker_connections, because it's 
> > obvious that when limits are met, new requests won't come 
> > through and this leaves you with bad visitor experience.
> 
> It would be a good idea to clarify differences from limit_conn 
> module.  Right now it looks like use cases you consider are better 
> handled by limit_conn.

The difference is that limit_conn (from limit_zone module) limits the number of simultaneous connections PER IP. This is useful in many cases, but soflimit_module, as stated above, compares its limit with total number of active connections, which is different. For example, site can have 2000 different clients with 1 connection each, but backend can handle only 300 without performance issues. Actual limits of course vary from site to site.

> 
> Maxim Dounin
> 
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-- 
Zeljko Tomic <scyth at unixreich.com>