Difference between all_nodes VS cluster_nodes CouchDB 2.X cluster membership?

The _membership endpoint in CouchDB (http://user:pass@domain:5985/_membership ) returns the following json to me: { all_nodes: [ "couchdb@n1.domain.me", "couchdb@n2.domain.me", "couchdb@n3.domain.me" ], cluster_nodes: [ "couchdb@n1.domain.me", "couchdb@n2.domain.me", "couchdb@n3.domain.me" ] } When would all_nodes NOT be the same as cluster_nodes? I managed to setup a cluster incorrectly when building CouchDB from source - there were 3 nodes in 'all_nodes', but none in 'cluster_nodes'. An answer points to the Server Fault question BigCouch all_nodes vs cluster_nodes , where using BigCouch the question author found _membership returned a list of cluster_nodes but nothing in all_nodes. (So similar to the question I'm asking, although opposite to what I've seen where only all_nodes had values). I don't understand the answer: > I just heard from Robert Newson on IRC that BigCouch nodes are connected lazily. Because: 1. I thought I read in CouchDB somewhere that nodes to be online at the time they are added to a cluster; and 2. This is at best one reason why there may be differences in the all_nodes and cluster_nodes results. I'm effectively asking why there are 2 fields for what seems to be the same thing in CouchDB 2.x? My (very limited) experience is that a cluster that shows nodes in the all_nodes field but not in the cluster_nodes field doesn't work. It's either not an answer to this question, or so far above my level that I don't understand it.