Mongo::Error::NoServerAvailable: No primary server is available in cluster

ruby-on-rails docker mongoid

Verify you are able to connect to the nodes using the MongoDB shell (mongo binary). Most likely you do not have connectivity.
Set log level to debug (https://docs.mongodb.com/mongoid/master/tutorials/mongoid-configuration/#logging) which will tell you what the driver is doing as it is attempting to connect to the deployment.

CodeHunter