Open Stack

On 11/14/2012 12:28 PM, Eoghan Glynn wrote:
> 1. Extend the existing os-server-diagnostics API extension to expose
>    any additional stats that ceilo needs.
> 
>    +  would allow the ceilo compute agent to be scaled independently
>       of the nova-compute node (i.e. no need for a 1:1 correspondence)
>    -  the diagnostics returned are currently hypervisor-specific
>    -  the additional nova-api-->nova-compute RPC call would add lag
>       and impact timeliness for metrics gathering
> 
> 
> 2. Call the nova get_diagnostics RPC directly (as per the experimental
>    patch proposed by Yunhong Jiang https://review.openstack.org/15952),
>    or use a new RPC message specifically designed for this purpose.
> 
>    +/- as for #1, but also removes the lag involved in an additional
>        hop between nova services
>    -   calling RPC directly would expose ceilo to a much less stable
>        (i.e. rapidly rev'd) API than would be the case for #1

> So the question is how the nova domain experts see these options sizing
> up?
> 
> Personally I'm liking option #2, aside from a lingering concern about
> how rapidly RPC versioning is rev'd (which suggests the more sedate
> pace of API versioning would be easier to consume). Also some statement
> on whether RPC is envisaged as being externally-callable would be good.

I'm in favor of option #1.  This is primarily because I have been
considering all rpc APIs to be private internal nova APIs.

The benefit of #2 over #1 appears to be a performance concern.  How
sensitive to timing are these measurements?  Also, if they are very
sensitive, it seems you'd be facing the same risk of problems due to
delays using rpc directly, because the queues can certainly get backed
up, so #2 doesn't help much.

-- 
Russell Bryant