OK. If you are using Rails + MongoID and you get this error message here:
read_secondary options has now been deprecated and will be removed in driver v2.0. Use the :read option instead.
Than you just have to change your configuration. Just replace “read_secondary” with “read”.
Robert Reiz 
Check out the page here: https://github.com/mongoid/mongoid/issues/1368
And one more thing. “read” is not true or false. Valid values for “read” are “:primary” and “:secondary”.