django migrations multiple databases

router.py

class LegacyRouter:
    route_app_labels = {'legacy',}
    legacy_database = 'legacy'

    def db_for_read(self, model, **hints):
        if model._meta.app_label in self.route_app_labels:
            return self.legacy_database
        return None

    def db_for_write(self, model, **hints):
        if model._meta.app_label in self.route_app_labels:
            return self.legacy_database
        return None

    def allow_relation(self, obj1, obj2, **hints):
        return None

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        is_legacy_db = db == self.legacy_database
        is_legacy_app = app_label in self.route_app_labels
        if is_legacy_db:
            return is_legacy_app
        else:
            return not is_legacy_app

settings.py

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'producto',
    },
    'legacy': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'legacy-schema',
    }
}