SSH permissions error when resizing or migrating an instance (OpenStack)

If you are resizing or migrating an instance KVM, KVM for IBM z Systems®, or PowerKVM hypervisors, you might encounter an ssh ...Permission denied error.

In this situation, you must ensure that the hypervisors can ssh (as a Nova user) to each other by public key. To do so, complete the following steps:

Obtain a key pair (public key and private key). You can use the root key that is in the `/root/.ssh/id_rsa and /root/.ssh/id_ras.pub directories or you can generate a new key pair.
Run setenforce 0 to put SELinux into permissive mode.
Enable login abilities for the Nova user.
```
usermod -s /bin/bash nova
```
Now you can switch to the Nova account by using the following command.
```
su nova
```

Create the folder that is needed by ssh and place the private key that you obtained in step 1 into this folder.

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

Repeat steps 2-4 on each node.
Important: All the nodes share a key pair and you must not generate a new key pair for the second node.
Ensure that the key is working properly.
```
# su - nova
# ssh node-another
```
Note:
1. You log in to the node-another node without a password.
2. If your server is configured with both the IP address and the hostname, you must run this command twice. For example:
  1. su nova ssh nova@host-name
  2. su nova ssh nova@x.x.x.x
    where x.x.x.x is the server IP address.