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

[Michael DeHaan]

I've just implemented some changes in cobbler (cobblerd) and koan that 
allow for automatic remote service discovery using Avahi.
This allows for building of tools that rely on koan to be written in a 
way that doesn't need to be aware of where the cobbler server is,
which is particularly useful in multi-site operations.

The ultimate usage of this is the koan live CD or USB disk.   Now, with 
auto-discovery enabled, we can build a truly universal installer
image.   One image can install RHEL-4, F-7, whichever -- regardless of 
your location.   The live installer CD will boot in any (supported) bare
metal machine, check the machine's MAC address, find the cobbler server 
automatically, and install whatever profile is mapped to the MAC
address inside of cobbler.    None of this requires a PXE setup, either 
-- so it's easy to set up "bonus" install servers even if your organization
already has a PXE infrastructure.

To use this, install cobbler and koan from source, and also install the 
avahi-tools package on both ends.   That's all you need to do.
This will be included in the 0.6.1 release, when that happens.

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

--Michael