Upgrading from 0.6 to 0.9, REPLICA_DATABASE KeyError

[mikelane]

Everything worked fine with v0.6 and the following:

DATABASES = {
    'default': {
        'ENGINE': 'django.contrib.gis.db.backends.postgis',
        'HOST': os.getenv('DB_HOST'),
        'NAME': os.getenv('DB_NAME'),
        'USER': os.getenv('DB_USER'),
        'PASSWORD': os.getenv('DB_PASSWORD'),
        'CONN_MAX_AGE': None,
    },
    'readonly': {
        'ENGINE': 'django.contrib.gis.db.backends.postgis',
        'HOST': os.getenv('RO_DB_HOST') or os.getenv('DB_HOST'),
        'NAME': os.getenv('RO_DB_NAME') or os.getenv('DB_NAME'),
        'USER': os.getenv('RO_DB_USER') or os.getenv('DB_USER'),
        'PASSWORD': os.getenv('RO_DB_PASSWORD') or os.getenv('DB_PASSWORD'),
        'CONN_MAX_AGE': None,
    },
}
# configure readonly slaves https://github.com/jbalogh/django-multidb-router#masterslaverouter
SLAVE_DATABASES = ['readonly']
DATABASE_ROUTERS = ('multidb.MasterSlaveRouter',)

But with v0.9 and only the following changes:

# configure readonly slaves https://github.com/jbalogh/django-multidb-router#replicarouter
REPLICA_DATABASES = ['readonly']
DATABASE_ROUTERS = ('multidb.ReplicaRouter',)

I get the following error:

.venv/lib/python3.6/site-packages/django/db/models/manager.py:82: in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
.venv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py:565: in get_queryset
    return self._apply_rel_filters(queryset)
.venv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py:541: in _apply_rel_filters
    db = self._db or router.db_for_read(self.model, instance=self.instance)
.venv/lib/python3.6/site-packages/django/db/utils.py:258: in _route_db
    chosen_db = method(model, **hints)
.venv/lib/python3.6/site-packages/multidb/__init__.py:114: in db_for_read
    return get_replica()
.venv/lib/python3.6/site-packages/multidb/__init__.py:86: in get_replica
    return next(_get_replica_list())
.venv/lib/python3.6/site-packages/multidb/__init__.py:78: in _get_replica_list
    settings.DATABASES[db].get('TEST', {})['MIRROR'] = DEFAULT_DB_ALIAS
E   KeyError: 'readonly'

It looks to me like it isn't finding the database named 'readonly', but this only happens when we change the names as per the deprecation warning.