[et-mgmt-tools] Service discovery for cobbler and koan with Avahi

[Peter Wright]

Michael DeHaan wrote:
>
> Peter Wright wrote:
> > David Lutterkort wrote:
> >>
> >> On Fri, 2007-08-17 at 13:53 -0400, Michael DeHaan wrote:
> >> > How does this work?
> >> >
> >> >     Cobblerd will detect the presence of avahi-tools when it starts
> >> up,
> >> > and will publish the service.
> >> >
> >> >     With koan, we specify --server=DISCOVER to tell koan it needs to
> >> > probe for a cobbler server.
> >> >
> >> > For instance, the following command works regardless of where you 
> are:
> >> >   >     koan --server=DISCOVER --list-profiles
> >>
> >> Cool .. how about the following behavior: when koan is started without
> >> --server, it first tries to look up a host named 'cobbler' and uses 
> that
> >> as the cobblerd; if no such host exists, try to discover using 
> avahi; if
> >> that fails tell the user they are dumb and need to give na explicit
> >> server with --server ?
> >>
> > please do not put any hard coded hostnames in the koan code base.  two
> > immediate problems crop to mind:
> >
> > 1) a host named cobbler already exists and does not run cobblerd
> > 2) the system becomes coupled to a working DNS system
> >
> >
> > -p
> >
> >
> >
>
>
> Peter,
>
> I'm not so sure I agree a few defaults is a bad thing, since it's pretty
> easy to test for cobblerd's presence (xmlrpc responding to certain
> method on certain port) and we wouldn't have to engage this check unless
> --server was omitted.  David's suggestion actually works pretty well to
> help out those running EL4 boot servers (where there is no Avahi) --
> which is probably the most likely platform for a boot server at this
> point.    Rest assured I have ruled out "nmap" as a discovery method :)
>
> And obviously if  we specify --server (as was mandatory before) we can
> skip all of those checks (so you don't need DNS in that case).
>
> --Michael
>
>
OK, I guess I understand the reasoning here - although I get a little 
worried when hostnames are hard coded into applications like this, I 
rarely like outside forces determining naming schemes :)

I'd feel more comfortable if koan looked for a COBBLER_SERVER 
environment variable (or something similar) to get the name of the 
master cobbler node on ones network, or subnet.  Maybe this variable 
could be taken as an override of the default "cobbler" hostname.  
Assuming that koan is going to be called via shell scripts or some other 
programmatic method in most environments this would also help admins who 
may need to rename machines or test code against development/staging 
cobbler servers.  maybe i'm off base in this assumption though.

I've got my anal retentive admin hat on today so take this with a grain 
of salt ;)
-p

-- 
Peter Wright
Systems Administrator
Sony Pictures Imageworks
wright at imageworks.com
www.imageworks.com