We have a sharded cluster setup with 2 shards.
We have already a database with sharding and tagging on it enabled.

Now we have the requirement for a new database that does not need to be sharded. But it should live on the same sharded cluster environment.

What I did so far is,

• connected to one mongos router
• created the database
• created a user in this database

I tried then to verify the user credentials. It only worked on one mongos. Not on the others.
I tried to created then the user again on one of the other mongos routers.
It worked on one, on the other I got the message the users already exists.

Our application that started writing data into a collection.
This collection is not visible on one mongos router. Probably the one where I first created the user.

Any idea why it's not visible on one mongos?

What is the correct way to have a unsharded database/collection on a sharded cluster?

Thanks
Marco