Routing to a certain worker

[Maxim Dounin]

Hello!

On Mon, Jul 23, 2018 at 01:53:21PM -0400, M.P. Ardhanareeswaran wrote:

> I understand the desire for worker processes to be symmetric.
> 
> ProxyPass and upstream allow sticky session/session affinity 
> which does introduce some skew though mighty useful IMHO.  
> 
> Do you have any thoughts about use of this?  
> 
> I am very new to handler development in NGINX.  It appears that 
> the handlers cannot do this and is heavily discouraged.

Normally, if a module needs some information to be shared between 
worker processes, it uses shared memory zones:

http://nginx.org/en/docs/dev/development_guide.html#shared_memory

Sticky sessions use shared memory and therefore do not introduce 
any inequalities between worker processes.  Many other modules, 
such as limit_conn and limit_req, do the same.

Unfortunately, your particular case as you've described it is 
different, as you are trying to open a database connection and 
keep it open for future requests.  Unless a connection is statless 
and can be re-opened on demand, this is won't be something 
possible to implement within nginx worker model, because there are 
no mechanisms to share connections between worker processes.

-- 
Maxim Dounin
http://mdounin.ru/