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From Ted Zlatanov <...@lifelogs.com>
Subject Re: finding Cassandra servers
Date Wed, 03 Mar 2010 16:05:49 GMT
On Wed, 3 Mar 2010 09:32:33 -0600 Gary Dusbabek <gdusbabek@gmail.com> wrote: 

GD> 2010/3/3 Ted Zlatanov <tzz@lifelogs.com>:
>> This requires knowledge of the seeds so I need to at least look in
>> storage-conf.xml to find them.  Are you saying there's no chance of
>> Cassandra nodes (or just seeds) announcing themselves, even if it's
>> optional behavior that's off by default?  If so I'll do the contrib mDNS
>> service but it really seems like a backward way to do things.

GD> Nodes already announce themselves, only just to the cluster.  That's
GD> what gossip is for.  I don't see the point of making the announcement
GD> to the subnet at large.

GD> The decision rests with the community.  Obviously, if there is enough
GD> merit to this work, it will find its way into the codebase.  I just
GD> think it falls into the realm of shiny-and-neat (mdns and automatic
GD> discovery is cool) and not in the realm of pragmatic (not reliable
GD> across subnets).

It's currently not possible to find a usable node without running
centralized services like RRDNS or a special mDNS broadcaster as you
suggested.  I don't think this is shiny and neat, it's a matter of
running in a true decentralized environment (which Cassandra is supposed
to fit into).

The subnet limitation is not an issue in my environment (we forward
much, much larger multicast volumes routinely) but I understand routing
multicasts is not everyone's cup of tea.  IMHO it's better than the
current situation and, mDNS being a well-known standard, can at least be
handled at the switch level without code changes.

I can do a patch+ticket for this in the core, making it optional and off
by default, or do the same for a contrib/ service as you suggested.  So
I'd appreciate a +1/-1 quick vote on whether this can go in the core to
save me from rewriting the patch later.

Ted


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