[Yum-devel] zeroconf-like discovery of repos

[Mihai Ibanescu]

Hello,

Here's a scenario that I've been thinking about, and wanted to get an idea how
useful it would be for other people.

I happen to have a local mirror of some yum repositories. Since the mirror is
behind the firewall, it's not accessible to the rest of the world, so no
reason for it to live on the mirrorlist.

However, if I plug my laptop in the network I'd like to get my updates from my
fast mirror, and if I go home I want to follow the regular route.

Me changing the file in yum.repos.d is sort of inconvenient. That's why I
think this would be a good case for service discovery.

The proposal I have is:
- each yum repository will have a unique name. For instance, Fedora Core would
  be core-fedora, Fedora Core Updates would be updates-core-fedora etc.
- the first thing that the client does for each repository is: do a SRV
  lookup for the yum repository name, plus _yum._tcp (ideally the domain name
  should be automatically filled in and it should come from dhcp). If the SRV
  lookup is successful, a secondary TXT lookup is performed, to retrieve the
  URL for that repository. The URL looks like the one in baseurl, minus the
  server name. So, for instance:

  SRV lookup of core-fedora._yum._tcp returns:
    download.fedora.example.com
  TXT lookip of core-fedora._yum._tcp returns:
    ('txtvers=1.0', 'path=/pub/fedora/linux/core/$releasever/$basearch/os')


Questions:
- Distinguishing the protocol for the repo: could be either a TXT record or
  the port for the SRV record. I'd vote for the former, since one can have an
  HTTP repo running on a non-standard port.
- This is based purely on a convention for carefully crafting the URLs. One
  could also "browse" the network and return a list of available yum repos -
  but I'd postpone that for a while.
- If we go this route, _yum will have to be registered as a 'service' with 
  dns-sd.org, see http://www.dns-sd.org/ServiceTypes.html

Does this sound useful?

Thanks,
Misa

Resources:
http://files.dns-sd.org/draft-cheshire-dnsext-dns-sd.txt
http://www.dns-sd.org/ServerStaticSetup.html
http://www.ietf.org/rfc/rfc2782.txt