Comment 9 for bug 1628216

Hitting this in the same environment Kevin was referring to, redeployed on 2.1.x and just upgraded to 2.2.1.1. In the below 172.31/16 is the private/OS mgmt network and 172.30.60/22 is the ipmi/pxe network.

jujumanage@maas:~$ juju run --unit=compute/4 'unit-get private-address'
172.31.1.195
FLEX-6.example.com. 30 IN A 172.31.1.195

jujumanage@maas:~$ juju run --unit nova-compute/24 "relation-ids cloud-compute"
cloud-compute:159
jujumanage@maas:~$ juju run --unit nova-compute/24 "relation-get -r cloud-compute:159 - nova-compute/24"
hostname: FLEX-6
migration_auth_type: ssh
nova_ssh_public_key: ssh-rsa xxxxkeyxxxx
  root@FLEX-6
private-address: 172.30.63.59
ssh_public_key: ssh-rsa aaaakeyaaaa root@FLEX-6

jujumanage@maas:~$ juju run --unit=nova-compute/24 'unit-get private-address'
172.31.1.195

Trying to migrate from FLEX-6 to:
FLEX-5 (nova-compute/21)
inet 172.31.1.189/16 brd 172.31.255.255 scope global bond0
inet 172.30.63.58/22 brd 172.30.63.255 scope global bond1

root@FLEX-6:~# ssh -vvvv -o BatchMode=yes 172.31.1.189 mkdir -p /var/lib/nova/instances/16981efa-f453-46ef-ab74-2ac8f77b503e
---snip---
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:XXXXXXXXXXXXXXXXXXXAcJE
debug3: hostkeys_foreach: reading file "/root/.ssh/known_hosts"
Host key verification failed.

root@FLEX-6:~# ssh -vvvv -o BatchMode=yes 172.30.63.58 mkdir -p /var/lib/nova/instances/16981efa-f453-46ef-ab74-2ac8f77b503e
Succeeds

Worked around for now by adding to all hypervisors /var/lib/nova/.ssh/config:
Host $relevant_host_pattern
    StrictHostKeyChecking no