[openstack-dev] [Nova] bp proposal: discovery of peer instances through metadata service

Justin Santa Barbara justin at fathomdb.com
Thu Jan 23 16:28:40 UTC 2014


Would appreciate feedback / opinions on this blueprint:
https://blueprints.launchpad.net/nova/+spec/first-discover-your-peers

The idea is: clustered services typically run some sort of gossip protocol,
but need to find (just) one peer to connect to.  In the physical
environment, this was done using multicast.  On the cloud, that isn't a
great solution.  Instead, I propose exposing a list of instances in the
same project, through the metadata service.

In particular, I'd like to know if anyone has other use cases for instance
discovery.  For peer-discovery, we can cache the instance list for the
lifetime of the instance, because it suffices merely to see instances that
were launched "before me".  (peer1 might not join to peer2, but peer2 will
join to peer1).  Other use cases are likely much less forgiving!

Justin
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