If you deploy many instances at the same time with the iSCSI driver the ironic-conductor can run out of memory suddenly because of the heavy memory usage from qemu-img {info, convert} calls. For example:
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager 'qemu-img', 'info', path)
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager File "/usr/lib/python2.7/site-packages/ironic_lib/utils.py", line 90, in execute
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager result = processutils.execute(*cmd, **kwargs)
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager File "/usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py", line 363
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager env=env_variables)
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager File "/usr/lib/python2.7/site-packages/eventlet/green/subprocess.py", line 54, in
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager subprocess_orig.Popen.__init__(self, args, 0, *argss, **kwds)
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager File "/usr/lib64/python2.7/subprocess.py", line 711, in __init__
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager errread, errwrite)
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager File "/usr/lib64/python2.7/subprocess.py", line 1224, in _execute_child
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager self.pid = os.fork()
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager OSError: [Errno 12] Cannot allocate memory
Jan 18 20:24:07 controller-0.localdomain ironic-conductor[161689]: 2017-01-18 20:24:07.084 161689 ERROR ironic.conductor.manager
Fix proposed to branch: master /review. openstack. org/422738
Review: https:/