Re: Pattern for multiple subservices and dynamic discovery i.e. VPN

[Oliver Schad <oliver.schad@automatic-server.com>]

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Dear Laurent,

thanks a lot for your quick response. I understand, that dynamic
discovery needs some thoughts to implement in an easy and flexible way.

Just to understand the requirements, if we want to implement that today:

- we need an scanning component for the desired state of running
  instances (something like 'find /etc/openvpn -name "*conf"')
- we need an scanning component for the current state in process list
- we need a diffing component
- we need a state applier component

A component could be a shell function. Applying state would mean to
fork and exec. A process tree would look like

/usr/bin/s6-svscan
 s6-supervise vpn-manager
   vpn-manager
     openvpn foo1.conf
     openvpn foo2.conf

Best Regards
Oli

On Wed, 17 Aug 2022 11:04:50 +0000
"Laurent Bercot" <ska-supervision@skarnet.org> wrote:

> >
> >I'm looking for a pattern to solve a problem, where you have to
> >discover dynamically the services you have to start.
> >
> >Examples could be VPN configurations, where you discover the
> >configuration files and start for every file an instance of the VPN
> >service.  
> 
>   Hi Oliver,
> 
>   Dynamic instantiation is a real pain point - it's an often requested
> feature, but it's surprisingly hard to make it work correctly and
> safely in a supervision scheme. Supervision works very well in static
> environments, but dynamic discovery is at odds with the architecture.
> 
>   I have a few ideas to mitigate that and help people create instanced
> services. Instantiation is a planned feature of the future s6-rc v1
> but it's still a ways away; I am also thinking of adding tools to help
> people handle instances with regular s6, amd they may come in the near
> future, but there are currently no such helpers, sorry.
> 
> --
>   Laurent
> 



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