Instances refer to the virtual machines that run inside the cloud on any physical compute node. These instances are managed by the compute services. A host is a node where a group of instances resides.  You can run several commands to work around with instances.  Command to pause an instance.  $ openstack server pause INSTANCE_NAME  Command to unpause an instance.  $ openstack server unpause INSTANCE_NAME  Command to suspend an instance.  $ openstack server suspend INSTANCE_NAME  Command to resume a suspended instance.  $ openstack server resume INSTANCE_NAME  Command to shutdown an instance and store it with corresponding data. Anything in memory is gone.  $ openstack server shelve SERVERNAME  Restore an instance.  $ openstack server unshelve SERVERNAME  Command to remove the instance and all data.   $ nova shelve-offload SERVERNAME  Command to soft reboot an instance.  $ openstack server reboot SERVER
Command to hard reboot an instance.  $ openstack server reboot --hard SERVER