Comment 1 for bug 1692430

Creation of cell0 cell is made here [1] , this cell creation takes the db value from [database]/connection value from your config file unless --database_connection is added into the command. This value is stored in nova_api db.

Excerpt from [2] :
If you are not going to pass the database url on the command line in step 3, you need to name the cell0 database based on the name of your existing Nova database: <Nova database name>_cell0.
Based of above, current {{ nova_database_name }}_cell0 is correct.

What I'm not sure is, how db sync for cell is handled, takes value from database=connection option or use the value stored in the nova_api db to sync the data, and how cell0 knows what db to use once set up. I think database=connection value is the correct way to handle this, and each cell points to it's connection name.

BTW, cell0 is an especial cell, is only used to store unscheduled or failed to schedule instances, is not a "real" functional cell.

[1] https://github.com/openstack/kolla-ansible/blob/master/ansible/roles/nova/tasks/simple_cell_setup.yml#L4
[2] https://docs.openstack.org/developer/nova/cells.html#cells-v2