I wanted to transfer (aka clone or copy) a strapi.io database that was using mongodb from one mongodb docker container to another mognodb docker container. Here is what I ended up with:

1. Enter the source docker container:

docker exec -it portal_mongo_1 bash

2. Use mongodump to create a database archive

mongodump --uri="mongodb://strapi@localhost:27017/portal?authSource=admin" --archive="mongodump-portal"

3. Exit and copy the archive from docker to host:

docker cp portal_mongo_1:/mongodump-portal .

4. Transfer the archive whenever the destination container is. For example in my case I used scp to copy it to another server.
5. Copy the archive from host to the destination docker:

docker cp mongodump-portal mongo1:/data

6. Enter the destination docker container:

docker exec -it mongo1 bash

7. Restore it using mongorestore:

mongorestore --uri="mongodb://username@localhost:27017/portal?authSource=admin" --archive="mongodump-portal" --nsFrom='portal.*' --nsTo='portal.*'