OpenStack - NoValidHost: No valid host was found
When creating a new instance within OpenStack you observe the following error,
==> /var/log/nova/nova-conductor.log <== ... u"RescheduledException: Build of instance xxx-yyy-zzz was re-scheduled: internal error: no supported architecture for os type 'hvm'\n"] ... NoValidHost: No valid host was found. There are not enough hosts available.
This due to running OpenStack within a virtual machine. As on the compute host you are trying to run KVM but the virtualisation extensions KVM require are not available .
To resolve the issue edit your /etc/nova/nova.conf to use qemu.