Comment 5 for bug 2027621

Verification done on MAAS 3.0.2.

In a HA deployment with 1 region+rack and 1 rack,
the dhcpd.conf file's section 'failover peer' has
IPv4+IPv6 address in 3.0.1 and only IPv4 in 3.0.2

The synthetic reproducer changes the order of IPs
in the maasdb so the IPv6 address has a _lower id_
than then IPv4 address (and thus goes first in the
for-loop in get_ip_address_for_rack_controller()).

(Steps are described in more detail in comment #3.)

Before DB changes:

 # maas admin rack-controllers read | jq '.[] | [.system_id, .hostname, (.interface_set[] | .links[] | [.id, .ip_address, .subnet.vlan.id])]'
 [
   "hy37ba",
   "maas-srv-30snap",
   [
     1,
     "10.30.200.2",
     5001
   ],
   [
     3,
     "fc00::2",
     5001
   ]
 ]
 [
   "8meq3e",
   "maas-srv-peer-30snap",
   [
     2,
     "10.30.200.3",
     5001
   ],
   [
     4,
     "fc00::3",
     5001
   ]
 ]

DB changes:

 # maas-test-db.psql
 postgres=# \c maasdb
 maasdb=# select id, ip from maasserver_staticipaddress order by id;
  id | ip
 ----+-------------
   1 | 10.30.200.2
   2 | 10.30.200.3
   3 | fc00::2
   4 | fc00::3
 (4 rows)

 maasdb=# update maasserver_staticipaddress set ip='1.2.3.4' where id=4;
 UPDATE 1
 maasdb=# update maasserver_staticipaddress set ip='fc00::3' where id=2;
 UPDATE 1
 maasdb=# update maasserver_staticipaddress set ip='10.30.200.3' where id=4;
 UPDATE 1

 maasdb=# select id, ip from maasserver_staticipaddress order by id;
  id | ip
 ----+-------------
   1 | 10.30.200.2
   2 | fc00::3
   3 | fc00::2
   4 | 10.30.200.3
 (4 rows)

 maasdb=# \q

After DB changes:

 # maas admin rack-controllers read | jq '.[] | [.system_id, .hostname, (.interface_set[] | .links[] | [.id, .ip_address, .subnet.vlan.id])]'
 [
   "hy37ba",
   "maas-srv-30snap",
   [
     1,
     "10.30.200.2",
     5001
   ],
   [
     3,
     "fc00::2",
     5001
   ]
 ]
 [
   "8meq3e",
   "maas-srv-peer-30snap",
   [
     2,
     "fc00::3",
     5001
   ],
   [
     4,
     "10.30.200.3",
     5001
   ]
 ]

MAAS 3.0.1:

 # snap list maas
 Name Version Rev Tracking Publisher Notes
 maas 3.0.1-10052-g.82c730c57 28871 3.0/stable canonical✓ -

 Enable DHCP with HA:

 root@maas-srv-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     primary;
     address 10.30.200.2;
     peer address fc00::3;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
     mclt 3600;
     split 255;
 }

 root@maas-srv-peer-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     secondary;
     address fc00::3;
     peer address 10.30.200.2;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
 }

 Disable/Re-enable DHCP with HA (switch the order of servers for testing purposes):

 root@maas-srv-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     secondary;
     address 10.30.200.2;
     peer address fc00::3;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
 }

 root@maas-srv-peer-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     primary;
     address fc00::3;
     peer address 10.30.200.2;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
     mclt 3600;
     split 255;
 }

MAAS 3.0.2:

 # snap refresh --channel=3.0/edge maas
 # snap list maas
 Name Version Rev Tracking Publisher Notes
 maas 3.0.2-10056-g.089ec66c2 33607 3.0/edge canonical✓ -

 Enable DHCP with HA:

 root@maas-srv-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     primary;
     address 10.30.200.2;
     peer address 10.30.200.3;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
     mclt 3600;
     split 255;
 }

 root@maas-srv-peer-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     secondary;
     address 10.30.200.3;
     peer address 10.30.200.2;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
 }

 Disable/Re-enable DHCP with HA (switch the order of servers for testing purposes):

 root@maas-srv-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     secondary;
     address 10.30.200.2;
     peer address 10.30.200.3;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
 }

 root@maas-srv-peer-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     primary;
     address 10.30.200.3;
     peer address 10.30.200.2;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
     mclt 3600;
     split 255;
 }

 Disable/Re-enable DHCP with HA (switch the order of servers for testing purposes):

 root@maas-srv-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     primary;
     address 10.30.200.2;
     peer address 10.30.200.3;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
     mclt 3600;
     split 255;
 }

 root@maas-srv-peer-30snap:~# sudo cat /var/snap/maas/common/maas/dhcpd.conf | sed -n '/^failover peer/,/^}/p'
 failover peer "failover-vlan-5001" {
     secondary;
     address 10.30.200.3;
     peer address 10.30.200.2;
     max-response-delay 60;
     max-unacked-updates 10;
     load balance max seconds 3;
 }