How do you check if the client for a MongoDB instance is valid?

Hi to find out that the connection is established or not you can do that :

from pymongo import MongoClient
from pymongo.errors import ConnectionFailure
client = MongoClient()
try:
   # The ismaster command is cheap and does not require auth.
   client.admin.command('ismaster')
except ConnectionFailure:
   print("Server not available")

serverSelectionTimeoutMS

This defines how long to block for server selection before throwing an
exception. The default is 30,000 (milliseconds). It MUST be
configurable at the client level. It MUST NOT be configurable at the
level of a database object, collection object, or at the level of an
individual query.

This default value was chosen to be sufficient for a typical server
primary election to complete. As the server improves the speed of
elections, this number may be revised downward.

Users that can tolerate long delays for server selection when the
topology is in flux can set this higher. Users that want to “fail
fast” when the topology is in flux can set this to a small number.

A serverSelectionTimeoutMS of zero MAY have special meaning in some
drivers; zero’s meaning is not defined in this spec, but all drivers
SHOULD document the meaning of zero.

https://github.com/mongodb/specifications/blob/master/source/server-selection/server-selection.rst#serverselectiontimeoutms

# pymongo 3.5.1
from pymongo import MongoClient
from pymongo.errors import ServerSelectionTimeoutError

client = MongoClient("mongodb://localhost:27000/", serverSelectionTimeoutMS=10, connectTimeoutMS=20000)

try:
    info = client.server_info() # Forces a call.
except ServerSelectionTimeoutError:
    print("server is down.")

# If connection create a new one with serverSelectionTimeoutMS=30000

serverSelectionTimeoutMS doesn’t work for me (Python 2.7.12, MongoDB 3.6.1, pymongo 3.6.0). A. Jesse Jiryu Davis suggested in a GitHub issue that we attempt a socket-level connection first as a litmus test. This does the trick for me.

def throw_if_mongodb_is_unavailable(host, port):
    import socket
    sock = None
    try:
        sock = socket.create_connection(
            (host, port),
            timeout=1) # one second
    except socket.error as err:
        raise EnvironmentError(
            "Can't connect to MongoDB at {host}:{port} because: {err}"
            .format(**locals()))
    finally:
        if sock is not None:
            sock.close()

# elsewhere...
HOST = 'localhost'
PORT = 27017
throw_if_mongodb_is_unavailable(HOST, PORT)
import pymongo
conn = pymongo.MongoClient(HOST, PORT)
print(conn.admin.command('ismaster'))
# etc.

There are plenty of problems this won’t catch, but if the server isn’t running or isn’t reachable, this’ll show you right away.

Can also be checked this way:

from pymongo import MongoClient
from pymongo.errors import OperationFailure

def check_mongo_connection(client_uri):
    connection = MongoClient(client_uri)

    try:
        connection.database_names()
        print('Data Base Connection Established........')

    except OperationFailure as err:
        print(f"Data Base Connection failed. Error: {err}")

check_mongo_connection(client_uri)

For pymongo >= 4.0 the preferred method is to use ping command instead of deprecated ismaster:

from pymongo.errors import ConnectionFailure
client = MongoClient()

try:
    client.admin.command('ping')
except ConnectionFailure:
    print("Server not available")

To handle auth failures, include OperationFailure:

except OperationFailure as err:
    print(f"Database error encountered: {err}")

Source: mongo_client.py

def mongo_available():
    maxsevseldelay = 1  # Assume 1ms maximum server selection delay
    client = pymongo.MongoClient('mongodb://localhost:27017,localhost2:27017',serverSelectionTimeoutMS=maxsevseldelay)
    try:
        # The ping command is cheap and does not require auth.
        client.admin.command('ping')
        return True, "Mongo connection working fine"
    except ConnectionFailure:
        return False, "Mongo Server not available"
        

mongo_available()
(False, 'Mongo Server not available')

This will loop for 30 seconds trying to ping to your deployment. Worked well for me.

# Connect to Mongo client
client = MongoClient(mongo_connection_string)

# Send a ping to confirm a successful connection
end_time = time.time() + 30
while time.time() < end_time:
    try:
        client.admin.command('ping')
        print("Pinged your deployment. You successfully connected to MongoDB!")
        break  # Successful connection, exit the loop
    except Exception as e:
        print(f"Failed to connect: {e}")