This is in reference to https://jira.mongodb.org/browse/RUBY-1281 ticket. I have added the db configuration and what error I think prevails.
 
I am trying to upgrade the mongo gem from 2.4.3 to 2.9.0. In the process, when I try to use a replica set, I am getting an issue in writing to the database. The reads are however fine.
 
When going through the code for server selection in selectable.rb, the select_server action, I see that select(cluster.servers) action call returns an empty array in case of selecting a server to write to.
 
My database configuration is:
 
{
  "default"=>
      {
         "database"=>"test_database",
         "hosts"=>["localhost:27018", "localhost:27019", "localhost:27020"],
         "options"=>{
                "read"=>

{                       "mode"=>:secondary_preferred                  }

,
                 "max_pool_size"=>1,
                 "connect"=>:replica_set,
                 "replica_set"=>"rs0",
                 "platform"=>"mongoid-6.2.1"
         }
     }
}