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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