Re: Holidays Brainstorming: instanced supervision

From: Olivier Brunel <jjk_at_jjacky.com>
Date: Wed, 13 Jan 2016 18:50:11 +0100

On Fri, 25 Dec 2015 11:43:31 +0100
Laurent Bercot <ska-supervision_at_skarnet.org> wrote:

> Hello everyone, and happy holidays!
>
> In the past few years, there have been some bits and pieces of
> discussion about "instanced services", i.e. some kind of supervised
> service that would be able to create different instances of the
> process at will. But it never got very detailed.
>
> I'd like to ask you: if you feel that instanced services are
> useful, what functionality would you like to see ? Concretely,
> practically, what do you want to be able to do ?
>
> Please stay away from mechanism and implementation details;
> I'm just trying to get a very high-level, conceptual feel for it
> at the moment - "what", as opposed to "how".
>
> Thanks !
>

Hey,

So I'm not sure this is what you're thinking of, but I can describe
what "instanced services" are with regards to anopa; And that's
basically just a way to use the same servicedir for multiple services,
or more exactly only create/manage a single servicedir, but be able to
use it for more than one services (or instances).

Can be helpful when you have multiple instances of "the same"/similar
services, where the only difference would be an argument to the daemon
or something to that effect.

This gets into mechanism I'm afraid, but I'm not sure how to best
explain it otherwise: servicedirs would be created/managed in a
sourcedir, and enabling (or compiling, might be the equivalent in
s6-rc) means pretty much copying the servicedir from the sourcedir into
the scandir (or compiled, or whatever), where it becomes "active"/in
use.

With instanced services, it means when you enable such a service you
add/specify an instance name. So e.g. the servicedir is "getty_at_" but
you enable "getty_at_tty2" -- which just means the servicedir getty@ is
copied under a different name in the scandir.

The intent being that to enable another getty, you just enable
getty_at_tty3 and that's it. One actual servicedir is being maintained,
but used many times (as different instances, which really are
different services in the end). If you need to fix/change the
servicedir, it's done once and then applied to all instances.

(Obviously the scripts (e.g. run) needs a way to use the instance name,
as that usually ends up being an argument to the daemon, or to point
to/read from a different config directory, etc)

Note that this actually isn't limited to longruns, but also works for
oneshots. Hence why I'm thinking this might be different to what you're
thinking of.

Anyhow, HTH
-j
Received on Wed Jan 13 2016 - 17:50:11 UTC