I wanted to load the production with fixture data from my local database. One of the possible solutions was copying to the volume from the local database and then restoring it in the production one.
The line under volumes copies the files in the dbdump to the docker-entrypoint-initdb.d
docker-entrypoint-initdb.d is a default folder created under the mongo volumes.
Then in the production one, you can communicate with a container using the exec -it command as mentioned here and do a mongorestore
Hope this helps!