CODEWITHSUNDEEP
pythonmongodbpymongo
Leeren
Leeren

Reputation: 2081

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

In particular, I am currently trying to check if a connection to a client is valid using the following function:

def mongodb_connect(client_uri):
    try:
        return pymongo.MongoClient(client_uri)
    except pymongo.errors.ConnectionFailure:
         print "Failed to connect to server {}".format(client_uri)

I then use this function like this:

def bucket_summary(self):
    client_uri = "some_client_uri"
    client = mongodb_connect(client_uri)
    db = client[tenant_id]
    ttb = db.timebucket.count() # If I use an invalid URI it hangs here

Is there a way to catch and throw an exception at the last line if an invalid URI is given? I initially thought that's what the ConnectionFailure was for (so this could be caught when connecting) but I was wrong.

If I run the program with an invalid URI, which fails to run, issuing a KeyboardInterrupt yields:

File "reportjob_status.py", line 58, in <module>
tester.summarize_timebuckets()
File "reportjob_status.py", line 43, in summarize_timebuckets
ttb = db.timebucket.count() #error
File "/Library/Python/2.7/site-packages/pymongo/collection.py", line   1023, in count
return self._count(cmd)
File "/Library/Python/2.7/site-packages/pymongo/collection.py", line 985, in _count
with self._socket_for_reads() as (sock_info, slave_ok):
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
File "/Library/Python/2.7/site-packages/pymongo/mongo_client.py", line 699, in _socket_for_reads
with self._get_socket(read_preference) as sock_info:
File  "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
File "/Library/Python/2.7/site-packages/pymongo/mongo_client.py", line 663, in _get_socket
server = self._get_topology().select_server(selector)
File "/Library/Python/2.7/site-packages/pymongo/topology.py", line 121, in select_server
address))
File "/Library/Python/2.7/site-packages/pymongo/topology.py", line 106, in select_servers
self._condition.wait(common.MIN_HEARTBEAT_INTERVAL)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 358, in wait
_sleep(delay)

Upvotes: 70

Views: 95113

Answers (8)

Ayub Abdi
Ayub Abdi

Reputation: 11

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}")

Upvotes: 0

ankuj
ankuj

Reputation: 21

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')

Upvotes: 0

Cas
Cas

Reputation: 6654

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

Upvotes: 0

nurealam siddiq
nurealam siddiq

Reputation: 1623

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)

Upvotes: 0

ESV
ESV

Reputation: 7730

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.

Upvotes: 2

The Demz
The Demz

Reputation: 7362

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

Upvotes: 5

Manochehr Rasouli
Manochehr Rasouli

Reputation: 689

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")

Upvotes: 31

Sylvain Leroux
Sylvain Leroux

Reputation: 52030

The serverSelectionTimeoutMS keyword parameter of pymongo.mongo_client.MongoClient controls how long the driver will try to connect to a server. The default value is 30s.

Set it to a very low value compatible with your typical connection time¹ to immediately report an error. You need to query the DB after that to trigger a connection attempt :

>>> maxSevSelDelay = 1 # Assume 1ms maximum server selection delay
>>> client = pymongo.MongoClient("someInvalidURIOrNonExistantHost",
                                 serverSelectionTimeoutMS=maxSevSelDelay)
//                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> client.server_info()

This will raise pymongo.errors.ServerSelectionTimeoutError.

¹ Apparently setting serverSelectionTimeoutMS to 0 might even work in the particular case your server has very low latency (case of a "local" server with very light load for example)

It is up to you to catch that exception and to handle it properly. Something like that:

try:
    client = pymongo.MongoClient("someInvalidURIOrNonExistantHost",
                                     serverSelectionTimeoutMS=maxSevSelDelay)
    client.server_info() # force connection on a request as the
                         # connect=True parameter of MongoClient seems
                         # to be useless here 
except pymongo.errors.ServerSelectionTimeoutError as err:
    # do whatever you need
    print(err)

will display:

No servers found yet

Upvotes: 93

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