Re: Proposal: auto-instantiate services with a default value

[Ludovic Courtès]

Hi,

Danny Milosavljevic <address@hidden> skribis:

> On Tue, 09 Jan 2018 10:05:34 +0100
> address@hidden (Ludovic Courtès) wrote:
>
>> We discussed some time ago the possibility to automatically instantiate
>> services.  Now that service types have default value, I think it’s a
>> viable approach: if a service is required, and *if* it provides a
>> default value, then we can automatically instantiate it.
>> 
>> So in the example above, you’d just specify ‘rottlog-service-type’ and
>> an ‘mcron-service-type’ would be automatically added if it’s not already
>> there.
>
> Yes, as long as there's a way for the user to easily see what it instantiated 
> (in the running system).

‘operating-system-services’ would still only lists services that have
been explicitly specified, but ‘guix system extension-graph’ would show
everything.

> Also, that means that the instantiated mcron-service would automatically get 
> a rottlog entry even though the mcron-service-types's default job list is 
> empty, right ?

Correct.

> In that case it would be nice to be able to (optionally) override this 
> mcron-service by a custom mcron-service in /etc/config.scm but retain the 
> modified configuration with the implicit job in it.  Is that possible?

Sure, the current way to do things (which is to explicitly list rottlog
*and* mcron) would remain valid, and you could pass your own mcron
config this way.

Ludo’.