create index on existing collection on a MongoDB replica set (PRIMARY)

Question

I want to add an index on an existing collection in a MongoDB replica set. This replica set has only a Primary, at the moment, and is configured in this way to be able to use MongoDB change streams.
I log into Mongo shell using:
mongo -u <Account>
where <Account> is an account with role 'userAdminAnyDatabase '.
Then issue the commands:

use dbOfInterest 
db.collectionOfInterest.createIndex({fieldOne:-1})

But after issuing the command above the console seems not responding anymore (after several minutes I had to stop it using CTRL+C).
The considered collection is a test one with very few documents.
What am I doing wrong?

Answer 1

What you do is creating index "foreground" and that blocks usage of DB, until creation is ready. You need to do it "background".

db.collectionOfInterest.createIndex({fieldOne:-1},{background:1})