Sequence of events that lead to the problem:

1. In db node, nodeg6, due to following trace, nova logs grew to 30+GB and took complete available disk space..
2. This left cassandra process in a bad state, while the status showed ACTIVE, it was not listening to port 9160
3. The setup was running with 2 DB nodes; With one DB node down, read & write consistency quorum was not met ..
3. Due to above issue, discovery & API services started seeing error [listed in previous post]

Actions to be taken:
a. For R1.10, db nodes should be in odd numbers; In case of upgrade from previous releases, this should be addressed first .. 
b. Discovery needs to address the issue in error code path
c. We should show correct state of DB process..

2014-08-29 06:25:02.107 30834 TRACE nova.openstack.common.rpc.common ConnectionError: 530: (NOT_ALLOWED - attempt to reuse consumer tag '1', (60, 20), None)
2014-08-29 06:25:02.107 30834 TRACE nova.openstack.common.rpc.common
2014-08-29 06:25:02.108 30834 INFO nova.openstack.common.rpc.common [-] Reconnecting to AMQP server on 10.204.217.46:5672
2014-08-29 06:25:02.117 30834 INFO nova.openstack.common.rpc.common [-] Connected to AMQP server on 10.204.217.46:5672
2014-08-29 06:25:02.118 30834 ERROR nova.openstack.common.rpc.common [-] Failed to consume message from queue: 530: (NOT_ALLOWED - attempt to reuse consumer tag '1', (60, 20), None)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common Traceback (most recent call last):
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/nova/openstack/common/rpc/impl_kombu.py", line 577, in ensure
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     return method(*args, **kwargs)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/nova/openstack/common/rpc/impl_kombu.py", line 655, in _consume
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     queues_tail.consume(nowait=False)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/nova/openstack/common/rpc/impl_kombu.py", line 191, in consume
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     self.queue.consume(*args, callback=_callback, **options)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/kombu/entity.py", line 595, in consume
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     nowait=nowait)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/amqp/channel.py", line 1769, in basic_consume
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     (60, 21),  # Channel.basic_consume_ok
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/amqp/abstract_channel.py", line 69, in wait
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     self.channel_id, allowed_methods)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/amqp/connection.py", line 237, in _wait_method
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     self.wait()
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/amqp/abstract_channel.py", line 71, in wait
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     return self.dispatch_method(method_sig, args, content)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/amqp/abstract_channel.py", line 88, in dispatch_method
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     return amqp_method(self, args)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common   File "/usr/lib/python2.7/dist-packages/amqp/connection.py", line 491, in _close
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common     raise ConnectionError(reply_code, reply_text, (class_id, method_id))
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common ConnectionError: 530: (NOT_ALLOWED - attempt to reuse consumer tag '1', (60, 20), None)
2014-08-29 06:25:02.118 30834 TRACE nova.openstack.common.rpc.common
2014-08-29 06:25:02.119 30834 INFO nova.openstack.common.rpc.common [-] Reconnecting to AMQP server on 10.204.217.46:5672