The three config servers were migrated to CSRS and WiredTiger last week. Followed the documentation here : https://docs.mongodb.com/manual/tutorial/upgrade-config-servers-to-replica-set/

Since the change, when connected to a mongoS, we cannot see the databases after using show dbs and we cannot connect using --authenticationDatabase admin --username root --password xxxxx --authenticationMechanism SCRAM-SHA-1

There are no errors in any logs, neither mongos, on the config servers, on the mongod machines. rs.conf and rs.status are OK. The mongos have been stopped and restarted a few times to try and rectify this, with no luck.

  • 3 things if you have not checked already. All binaries in the sharded clusters must be at least version 3.2.4. The config server must use the same port as before. Do not add existing config servers to the replica set,Use new dbpaths for the new instances. Nov 20, 2017 at 15:16
  • We're using 3.2.5. The config servers now use different ports. Except during the initial migration of the to-be primary in the CSRS, if using the same machines, I don't see how it is possible to use the same ports. New dbpaths have been used. Nov 20, 2017 at 16:39
  • What sh.status() says? If you can give that command. When you "try" to connect to mongoS, what is error message of mongo -command? If you look mongos log, do they report successful connection to config and mongod servers?
    – JJussi
    Nov 21, 2017 at 5:31

1 Answer 1


There were no errors during the migration process. BUT a NEW dbpath was used so the initial config server didn't use the existing details but in fact created 'empty' details in the new dbpath.

Basically when doing the migration, the first cfg server does not change it's dbpath nor it's port throughout the migration procedure. Personally I found this unclear in the procedure, especialy when you are migration from SCCC to CSRS and using WiredTiger.

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