I have a simple config on single host virtualbox. It is running on ubuntu 12.04 folsom. Instances are started up but then shutoff.

I can see the system is starting instance :

==> /var/log/libvirt/libvirtd.log <==
2013-05-16 12:07:01.984+0000: 1542: info : qemudDomainDefine:4943 : Creating domain 'instance-00000035'

==> /var/log/syslog <==
May 16 14:07:02 openstack1 kernel: [ 7515.451862] type=1400 audit(1368706022.524:35): apparmor="STATUS" operation="profile_load" name="libvirt-badd461b-65cf-42c6-ae8e-79ac58788f0c" pid=16439 comm="apparmor_parser"

==> /var/log/libvirt/libvirtd.log <==
2013-05-16 12:07:02.718+0000: 1544: info : virNetDevProbeVnetHdr:94 : Enabling IFF_VNET_HDR

==> /var/log/syslog <==
May 16 14:07:02 openstack1 kernel: [ 7515.661317] device vnet0 entered promiscuous mode
May 16 14:07:02 openstack1 kernel: [ 7515.661734] br100: port 2(vnet0) entered forwarding state
May 16 14:07:02 openstack1 kernel: [ 7515.661747] br100: port 2(vnet0) entered forwarding state

==> /var/log/libvirt/libvirtd.log <==
2013-05-16 12:07:04.405+0000: 1544: info : virSecurityDACSetOwnership:99 : Setting DAC user and group on '/var/lib/nova/instances/instance-00000035/disk' to '108:115'
2013-05-16 12:07:04.406+0000: 1544: info : virSecurityDACSetOwnership:99 : Setting DAC user and group on '/var/lib/nova/instances/_base/4757b7884a99bab0217593574304c51408fbeeac' to '108:115'
2013-05-16 12:07:04.406+0000: 1544: info : virSecurityDACSetOwnership:99 : Setting DAC user and group on '/var/lib/nova/instances/instance-00000035/console.log' to '108:115'
2013-05-16 12:07:04.406+0000: 1544: info : virSecurityDACSetOwnership:99 : Setting DAC user and group on '/var/lib/nova/instances/instance-00000035/kernel' to '108:115'

==> /var/log/nova/nova-compute.log <==
2013-05-16 14:07:06 INFO nova.virt.libvirt.connection [-] [instance: badd461b-65cf-42c6-ae8e-79ac58788f0c] Instance spawned successfully.

I can see briefly interface comming up :

bridge name     bridge id               STP enabled     interfaces
br100           8000.fa163e532cac       no              vlan100
                                                        vnet0
virbr0          8000.000000000000       yes

but then I see this error :

==> /var/log/libvirt/libvirtd.log <==
2013-05-16 12:07:12.773+0000: 1535: error : qemuMonitorIO:603 : internal error End of file from monitor

==> /var/log/syslog <==
May 16 14:07:12 openstack1 kernel: [ 7525.692084] br100: port 2(vnet0) entered disabled state
May 16 14:07:12 openstack1 kernel: [ 7525.698131] device vnet0 left promiscuous mode
May 16 14:07:12 openstack1 kernel: [ 7525.698137] br100: port 2(vnet0) entered disabled state

==> /var/log/libvirt/libvirtd.log <==
2013-05-16 12:07:12.832+0000: 1535: error : virNetDevGetIndex:656 : Unable to get index for interface vnet0: No such device

My understanding is that libvirt (qemu) fail on starting the instance when trying to bring up interface on the bridge (br100). I really dont understand why it is failing. Can somebody help ?

Here is nova.conf :

--dhcpbridge_flagfile=/etc/nova/nova.conf
--dhcpbridge=/usr/bin/nova-dhcpbridge
--logdir=/var/log/nova
--state_path=/var/lib/nova
--lock_path=/var/lock/nova
--force_dhcp_release
--iscsi_helper=tgtadm
--libvirt_use_virtio_for_bridges
--connection_type=libvirt
--root_helper=sudo nova-rootwrap
--ec2_private_dns_show_ip
--sql_connection=mysql://nova:openstack@172.16.0.1/nova
--use_deprecated_auth
--s3_host=172.16.0.1
--rabbit_host=172.16.0.1
--ec2_host=172.16.0.1
--ec2_dmz_host=172.16.0.1
--public_interface=eth1
--image_service ...