[GitHub] [couchdb] rnewson commented on issue #2382: CouchDB backup instance - zones vs replicas?

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rnewson commented on issue #2382: CouchDB backup instance - zones vs replicas?
URL: https://github.com/apache/couchdb/issues/2382#issuecomment-569463365
 
 
   As Nick has noted, Erlang expect low latency between nodes and there is only minimal security for that traffic by default (it's not encrypted), so you should not typically span datacenters (though see below) or geographical regions within a couchdb cluster. For inter-cluster data sync, use replication (over https).
   
   The "r" and "w" config parameters are ignored by the system these days and are calculated from "n" (as n/2+1). You can override with query parameters but it is not recommended. The properties you think will be guaranteed by this will not be (and, as per my first paragraph, the cluster topology you would be using is both badly performing and insecure).
   
   On zones, these exist to help map the shards (q*n) of a database evenly across failure domains. In practice this would be nodes in adjacent datacenters with very good low-latency connectivity (think AWS zone), for the purpose of surviving a datacenter failure. 

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