I have deployed mongodb as a StatefulSets on the K8S. It is not connecting, when I try to connect the DB using connection string URI(Ex: mongodb://mongo-0.mongo:27017,mongo-1.mongo:27017/cool_db), but it is connecting and getting the results when I use Endpoint IP Address.

# kubectl get sts
NAME    READY   AGE
mongo   2/2     7h33m

#kubectl get pods
NAME                                      READY   STATUS    RESTARTS   AGE
mongo-0                                   2/2     Running   0          7h48m
mongo-1                                   2/2     Running   2          7h47m

# kubectl get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)     AGE
kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP     10h
mongo        ClusterIP   None         <none>        27017/TCP   7h48m

I'm trying to test the connection using connection string URI in the python using the below process but it fails.

>>> import pymongo
>>> client = pymongo.MongoClient("mongodb://mongo-0.mongo:27017,mongo-1.mongo:27017/cool_db")
>>> db = client.cool_db
>>> print db.cool_collection.count()
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "/usr/lib64/python2.7/site-packages/pymongo/collection.py", line 1800, in count
   return self._count(cmd, collation, session)
 File "/usr/lib64/python2.7/site-packages/pymongo/collection.py", line 1600, in _count
   _cmd, self._read_preference_for(session), session)
 File "/usr/lib64/python2.7/site-packages/pymongo/mongo_client.py", line 1454, in _retryable_read
   read_pref, session, address=address)
 File "/usr/lib64/python2.7/site-packages/pymongo/mongo_client.py", line 1253, in _select_server
   server = topology.select_server(server_selector)
 File "/usr/lib64/python2.7/site-packages/pymongo/topology.py", line 235, in select_server
   address))
 File "/usr/lib64/python2.7/site-packages/pymongo/topology.py", line 193, in select_servers
   selector, server_timeout, address)
 File "/usr/lib64/python2.7/site-packages/pymongo/topology.py", line 209, in _select_servers_loop
   self._error_message(selector))
pymongo.errors.ServerSelectionTimeoutError: mongo-0.mongo:27017: [Errno -2] Name or service not known,mongo-1.mongo:27017: [Errno -2] Name or service not known

If we use the Endpoint IP Address, then we will get a response from DB.

>>> import pymongo
>>> client = pymongo.MongoClient("mongodb://10.244.1.8,10.244.2.9:27017/cool_db")
>>> db = client.cool_db
>>> print db.cool_collection.count()
0
>>> 

I have tried with different URI's like (client = pymongo.MongoClient("mongodb://mongo-0.mongo:27017/cool_db") )but not working. Could anyone please help me?