Openstack reliability test fails

Hi every one;
I had installed Openstack multi node using RDO Packstack method, and during the installation everything goes perfect, my setup was one controller node and three compute nodes each of them on separate physical PC ,I launched one instance and Openstack chose compute 1 as a host for this instance and when I disconnected compute 1 from network the openstack controller did not discover that compute 1 is down , until 1 minute passed the compute1 shows as down in horizon dashboard but the instance still down , and I cannot ping or access to instance my questions is :

1-why it is take long time ( about 1 minute ) for controller to discover that one of compute is down or not reachable

2- and why the instance is still down as I know ((when a computing node is faulty the system automatically move computing task from the faulty computing node to other computing nodes )) so in our case the system should move instance from faulty compute 1 to compute 2 or compute 3

thanks and best regards