[Swift-devel] changes

[Mihael Hategan]

On Sun, 2014-07-06 at 17:20 -0500, Tim Armstrong wrote:
> > Currently the configuration comes from the client. There is a plan to
> > have a version of the coaster service where the service is started with
> > an immutable configuration. This is a relatively different issue. It
> > does not need a hierarchical configuration format, and it will most
> > likely be a flat properties file. So if that addresses the problem
> > from /T's perspective, then things should be fine.
> 
> I don't think I understand well enough what the pros/cons are here.  With
> the static configuration, we'd lose the ability for the client to
> dynamically add new sites

Adding a site, in the sense of a new machine, won't affect services on
other machines. So this would be a separate issue. Think of coasters as
a faster GRAM. There is no provision for automatically managing a pool
of clusters in there.

>  or modify other settings

Right. You would lose the ability to modify settings at will from the
client.

>  - is that the only
> difference?  I understand that it maybe buys you some flexibility in that
> you can stand up a coasters service ahead of time, or reuse the same
> service for Swift runs with different configurations. I don't know if those
> are likely use cases for Swift/T.

I think standing up services ahead of time is the only possibility right
now, since the C client does not automatically start services.

>   Are there any Coasters settings where
> there's some other reason the client needs to set it?

Not that I can think of.

To summarize why I replied previously. You mentioned the coaster service
parsing its configuration. I'm stating that it's impossible to get both
flexibility and service-side parsing.

If the service is to load the configuration, then he client only
controls configuration to the extent that it could make a choices
between a number of pre-set configurations.

So if the service loads the configuration, that is less flexible than
when the client is able to tweak all the knobs. And for the client to be
able to do that based on some user specification, it needs to be able to
read that user specification. 

The bottom line is either server side parsing with the client having
limited control or client side parsing and that needs the client to be
able parse.

Mihael