Major Description
get_param change below renamed various parameters including the ones for rebalance internal settings.
https://github.com/couchbase/ns_server/commit/dcc892990702f1b5a6626fac037018761870584b
E.g. rebalance_moves_per_node, which is used to control # of concurrent backfills, was renamed to {ns_vbucket_mover, moves_per_node}.
However, when user changes these internal settings using RESTAPI, they are still being set as rebalance_moves_per_node. As a result, changing rebalance internal settings via REST API is broken.
http://src.couchbase.org/source/xref/trunk/ns_server/src/menelaus_web_settings.erl#85
One solution is to use the new names in menelaus_web_settings as well. E.g. replace rebalance_moves_per_node with {ns_vbucket_mover, moves_per_node} everywhere it is used.
But, it is possible that customers may have changed these parameters and it will break when they upgrade to Vulcan.
IMO, we should revert the get_param change for rebalance settings. Will let Aliaksey decide.
Also, it should be checked whether any other internal settings, other than the rebalance ones, are also affected.