Comment 5 for bug 1602400

If we document this in the API, we should really tell people to not use it, because it's a mess.

Basically there are no quota_classes in the database to start with. Quota values come from the defaults in nova.conf. However, if you update the quotas for the "default" quota class, then those are stuck in the database and preferred over the config options *AND* it's global, not per-tenant.

So if you updated default quotas for let's say instances, to 20, but didn't change quota_instances in your nova.conf, you'd still have a default quota for instances at 20 for all projects.

If you then change quota_instances=5 in nova.conf, but didn't update the 'default' quota class via the API, you'll still have a default quota of 20 for instances regardless of nova.conf.