If you try to run ironic-dbsync using default backend (SQLIte) you'll get the following error
(venv)viktors@devstack:~/ironic$ ironic-dbsync --config-file etc/ironic/ironic.conf.local
INFO [alembic.migration] Context impl SQLiteImpl.
INFO [alembic.migration] Will assume non-transactional DDL.
INFO [alembic.migration] Running upgrade None -> 2581ebaf0cb2, initial migration
INFO [alembic.migration] Running upgrade 2581ebaf0cb2 -> 21b331f883ef, Add provision_updated_at
INFO [alembic.migration] Running upgrade 21b331f883ef -> 3cb628139ea4, Nodes add console enabled
/home/viktors/ironic/.tox/venv/local/lib/python2.7/site-packages/alembic/util.py:189: UserWarning: Skipping unsupported ALTER for creation of implicit constraint
warnings.warn(msg)
INFO [alembic.migration] Running upgrade 3cb628139ea4 -> 31baaf680d2b, Add Node instance info
INFO [alembic.migration] Running upgrade 31baaf680d2b -> 3bea56f25597, add unique constraint to instance_uuid
CRITI [ironic] NotImplementedError: No support for ALTER of constraints in SQLite dialect
This happens because of SQLite ALTER limitations - see http:// www.sqlite. org/omitted. html