Hi, mongodb developers,

I want to convert the sharded cluster in our production environment to a replica set, but i don't want to change the connection uri in the application configuration.

Currently, i have two mongoses in the sharded cluster, so after migrate the data from sharded cluster to the new replica set, i would stop the mongoses and reuse the ip&ports of the original mongoses and set them to the primary and secondary member in the new replica set.

I hope the application would automatically connect to the replica set and work fine, but i'm not sure if this will work, so i made the a test to simulate the above situation.

—

Following is the sharded cluster deployed in a test environment,

• two mongoses: 100.81.164.181:9510, 100.81.164.181:9511

• two shards:

• 100.81.164.181:9791

• 100.81.164.181:9891

• config server: 100.81.164.181:9666

and  the replica set,

• 100.81.164.181:9510, 100.81.164.181:9511, 100.81.164.181:9512 (note: 100.81.164.181:9510 and 100.81.164.181:9511 is reused from mongoses)

and the test application code,

#!/usr/bin/python

import thread
import time
import logging
from pymongo import MongoClient
import sys

LOG_FORMAT = "%(asctime)s - %(levelname)s - %(message)s"
logging.basicConfig(level=logging.INFO, format=LOG_FORMAT)
client = MongoClient('mongodb://100.81.164.181:9510,100.81.164.181:9511/admin')

# Define a function for the thread
def write_read(threadName, delay):
    k = 0
    db = threadName + "-db"
    collection = threadName + "-collection"
    coll_handle = client[db][collection]
    while 1:
        try:
            time.sleep(delay)
            res = coll_handle.insert_one({'k': k, 'payload': 'xxxxxx'})
            logging.info("**%s** read after write: %s" % \
                         (threadName, str(coll_handle.find_one({'k': k}))))
            k = k + 1
        except Exception as e:
            logging.error("-- %s -- write_read mongo error: %s" % \
                          (threadName, str(e)))

# Create two threads as follows
thread_num = int(sys.argv[1])
try:
    for _ in xrange(0, thread_num):
        thread.start_new_thread(write_read, ("Thread-%d" % _, 1, ) )
except Exception as e:
    logging.error("Error: unable to start thread, %s.", str(e))

while 1:
    time.sleep(2)
    pass

start with: python test.py 20

Use 20 threads to continually write to and read from mongodb.

—

After stop the mongoses and start the replica set, the test code failed to connect to the replica set until i restarted it. The error message from the driver is,

No mongoses available

—

So, after changing the deployment behind the connection uri from sharded cluster to replica set, is there any way to let the mongo driver automatically identity this situation without a restart?

Please offer some help, thanks.