Hi,

my environment info:

centos-release.x86_64 7-7.1908.0.el7.centos
glusterfs.x86_64 6.8-1.el7
ovirt-engine.noarch 4.3.9.4-1.el7
ovirt-release43.noarch 4.3.9-1.el7

I have an external agent (openstack staging_oviirt) that powers on/off VMs during bulk install. See also here some other details:

I repeat many times the installation for test purposes and during these phases the application powers on (through ostacpm user) about 8 VMs in the same moment.

Sometimes it happens that one or more of them fail to start and in web admin gui I see this kind of sequence of events:

VM ostack-ceph2 was started by ostackpm@internal-authz (Host: ovirt.mydomain).
User <UNKNOWN> got disconnected from VM ostack-ceph2.
VM ostack-ceph2 is down with error. Exit message: Unable to add bridge vlan23 port vnet21: Device or resource busy.
Failed to run VM ostack-ceph2 on Host ovirt.mydomain
Failed to run VM ostack-ceph2  (User: ostackpm@internal-authz).

Soon I press the start button from web admin gui and the VM powers on without problems.

I think this kind of problem doesn't depend on the rest api agent.

Could it be a sort of bug or concurrency of power on commands?

If I grep VM UUID and name of the VM for the one above, I get this in engine.log:

On ovirt host I see:

2020-05-04 10:16:05,491+0200 ERROR (vm/38f806e7) [virt.vm] (vmId='38f806e7-5c48-4ffe-90e8-671b1a585256') The vm start process failed (vm:934)
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 868, in _startUnderlyingVm
    self._run()
  File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 2895, in _run
    dom.createWithFlags(flags)
  File "/usr/lib/python2.7/site-packages/vdsm/common/libvirtconnection.py", line 131, in wrapper
    ret = f(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/vdsm/common/function.py", line 94, in wrapper
    return func(inst, *args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 1110, in createWithFlags
    if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
libvirtError: Unable to add bridge vlan23 port vnet21: Device or resource busy
2020-05-04 10:16:05,492+0200 INFO  (vm/38f806e7) [virt.vm] (vmId='38f806e7-5c48-4ffe-90e8-671b1a585256') Changed state to Down: Unable to add bridge vlan23 port vnet21: Device or resource busy (code=1) (vm:1702)

Let me know if you meed more information

Gianluca