Description in customers words.
 
GO version : 1.13
 
mongo go-driver : 1.2.1
 

• Our go application is running on AWS-EKS. It is connecting to an Atlas instance. 
• As long as the ReplicaSet for the deployment is set to 1, everything works as expected..
• as soon as I change the ReplicaSet to 2 for my application deployment, the first instance (pod) of the application comes up successfully, but the second pod fails..
• it fails on executing line
      mgo, err = mongo.NewClient(options.Client().ApplyURI(uri))
• the value of uri is mongodb+srv://lockeradmin:XXXX@lockercluster-urwgb.mongodb.net
  I have masked the value of the password.
   
• the error I see is..
  error parsing uri: lookup mongodb.tcp.lockercluster-urwgb.mongodb.net on 172.20.0.10:53: read udp 10.53.8.160:49134->172.20.0.10:53: i/o timeout
   
  As part of debugging this, we launched a bare busybox image on the K8s cluster, loaded it with the mongo shell and tried to connect.. it did connect to the above instance successfully.
  Strangely, I have a SECOND service that runs on the same EKS cluster connecting to the same Atlas DB. And that app is also exhibiting the same behavior.
  However, I am able to successfully run 1 instance of each of the app successfully.