Feature requestED: monitoring Nginx from the outside

[Manlio Perillo]

François Battail ha scritto:
> I've almost finished the module (read: compilation reports no error) and want to
> take some time to discuss about some potential issues.
> 

Good.

> 1) Interaction with Nginx
> 
> [...]
 >
> 2) API
> 
> The API consist in one call:
> 
> void ngx_register_monitoring_value (ngx_str_t * name, ngx_atomic_t * value) ;
> 
> This function should be called by an Nginx module during it's initialization to
> tell the monitoring module that this variable should be added to the pool for
> watching.
> That's all. The module just continue to do what it wants with its ngx_atomic_t
> value, I will do the rest.
> 
> I may have some issue because my module has three states: initializing,
> registering, running so may be the order of modules may be problematic.
> 

When actually happens the running phase?
At the end of the HTTP request? At regular intervals?

Note that since you don't know when a variable will be updated, you may 
miss important changes in the variable.

As an example, in the upstream module if a peer is down, the variable 
peer.down will be set to 1, but if *all* the peers are down, then all 
the variables are set to 0, for a fast restart in the successive request.


> 
> 3) Configuration
> 
> [...]
 >
> 4) Scripts
> 
> A script should have read access to where nginx.pid is and will do the following
> pseudo code:
> 
> shm_id = ftok ("path.to.nginx.monitoring") ;
> mem = attach_to_shared_mem (shm_id) ;
> values = parse (mem)
> do_what_you_want_with_values (values)
> 

I can't see any form of synchronization here.

> 
> for example: update RRD databases, search for an anormal error count, search for
> an event unexpected...
> 
> It's no more my problem :-)
> 
> 
> 5) Conclusion
> 
> Dear List, tell me what you think and I will release soon this module (under A
> BSD-like licence of course) for review and comments.
> 
> Best regards.
> 



Regards   Manlio Perillo