Re: runit/dependencies

[Charlie Brady <charlieb-supervision@budge.apana.org.au>]

On Mon, 12 Jan 2004, Gerrit Pape wrote:

> Regarding all these ``I need support for dependencies'' (I've been asked
> often), and even work to provide straight dependencies with runit[0],
> I've yet to see a real example that cannot be handled by runit as it is
> currently.  It works for me.  All a service needs to do if another
> service it depends on isn't available, is to fail.

The key word here is "available". The exact semantics of "available" will
vary from service to service. The best that runit can provide is "has been
asked to start and hasn't failed yet". A service run script, OTOH, can
perform arbitrary probes of the "availability" of other services on which
it depends.

I consider the limited semantics of the status provided by "runsvstat" to
be a fatal obstacle to attempts to build dependency management into runit.  
All you can achieve is a slightly ordered parallel startup of multiple
services, with race conditions determining whether or not services start
successfully.

--
Charlie