Current code calling create_from_uri does not allow passing of options, which suggests that a URI with a replicaSet option should suffice for instantiating a client for a replica set. Instead, the cluster mode is standalone.

Bug RUBY-816 addresses merging options, which is obviously needed for options that are not part of the MongoDB URI spec. It also enables the user to supply :mode => :replica_set so that the cluster mode is instantiated correctly.

This raises the question of what is actually intended by the API for Client.new. The documentation is incomplete for addresses_or_uri and option :mode.