If you are resizing or migrating an instance between hypervisors, you
might encounter an SSH (Permission denied) error. Ensure that each node
is configured with SSH key authentication so that the Compute service
can use SSH to move disks to other nodes.

To share a key pair between compute nodes, complete the following
steps:

1. On the first node, obtain a key pair (public key and private
   key). Use the root key that is in the /root/.ssh/id_rsa and
   /root/.ssh/id_rsa.pub directories or generate a new key
   pair.

2. Run setenforce 0 to put SELinux into permissive
   mode.

3. Enable login abilities for the nova user:

   # usermod -s /bin/bash nova

   Ensure you can switch to the nova account:

   # su - nova

4. As root, create the folder that is needed by SSH and place the
   private key that you obtained in step 1 into this folder, and add the
   pub key to the authorized_keys file:

   mkdir -p /var/lib/nova/.ssh
   cp <private key>  /var/lib/nova/.ssh/id_rsa
   echo 'StrictHostKeyChecking no' >> /var/lib/nova/.ssh/config
   chmod 600 /var/lib/nova/.ssh/id_rsa /var/lib/nova/.ssh/authorized_keys
   echo <pub key> >> /var/lib/nova/.ssh/authorized_keys

5. Copy the whole folder created in step 4 to the rest of the
   nodes:

   # scp -r /var/lib/nova/.ssh remote-host:/var/lib/nova/

6. Ensure that the nova user can now log in to each node without
   using a password:

   # su - nova
   $ ssh *computeNodeAddress*
   $ exit

7. As root on each node, restart both libvirt and the Compute
   services:

   # systemctl restart libvirtd.service
   # systemctl restart openstack-nova-compute.service