Found with nodepool on the tripleo CI cloud - when the neutron floating IP quota is exhausted, novaclient add-floating-ip threw a generic 500.
ClientException: The server has either erred or is incapable of performing the requested operation. (HTTP 500) (Request-ID:
req-43db38fd-5b65-40be-960f-d00bf74e23b9)
/var/log/upstart/nova-api.log:2014-04-02 02:30:03.375 7736 ERROR nova.api.openstack [req-43db38fd-5b65-40be-960f-d00bf74e23b9
d5af62d2183d431796d74c5bb119ec9f e01e473a9250498883955b80966a1e58] Caught error: 409-{u'NeutronError': {u'message': u"Quota exceeded for
resources: ['floatingip']", u'type': u'OverQuota', u'detail': u''}}
was found in our logs - so this should be caught and rethrown appropriately.
Ib5320a13b5cc0c 493ef0763d0e2b4 575dc699bdf was meant to address this, or something similar, but doesn't seem to have.