Kea HA active-passive - the HA partnership flaps if a lease update is rejected because it is invalid

As reported in Support ticket #20651 and discussed with engineering. See also related issue #2409 (closed) .

2.0.0 (package)

This is the 'also-ran' issue, not the one dealing with the root cause, but we thought that we should consider if there is a better outcome after a lease update to an HA partner server is rejected.

Clearly the partner is present and operational. But it will not have a consistent picture of the state of address allocations if it is rejecting lease updates. What is the appropriate thing to do here?

Here's what's being logged (I believe on the primary):

2022-04-28 22:43:04.790 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_STATE_TRANSITION server transitions from HOT-STANDBY to WAITING state, partner state is PARTNER-DOWN
2022-04-28 22:43:04.790 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_LEASE_UPDATES_DISABLED lease updates will not be sent to the partner while in WAITING state
2022-04-28 22:43:04.790 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_LOCAL_DHCP_DISABLE local DHCP service is disabled while the dhcp-cpe-4b is in the WAITING state
2022-04-28 22:43:04.790 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_STATE_TRANSITION server transitions from WAITING to SYNCING state, partner state is PARTNER-DOWN
2022-04-28 22:43:04.790 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_LEASE_UPDATES_DISABLED lease updates will not be sent to the partner while in SYNCING state
2022-04-28 22:43:04.790 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_SYNC_START starting lease database synchronization with SERVER-NAME-REDACTED
2022-04-28 22:43:06.217 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_LEASES_SYNC_LEASE_PAGE_RECEIVED received 6823 leases from SERVER-NAME-REDACTED
2022-04-28 22:43:06.415 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_SYNC_SUCCESSFUL lease database synchronization with SERVER-NAME-REDACTED completed successfully in 1625.051 ms
2022-04-28 22:43:06.415 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_STATE_TRANSITION server transitions from SYNCING to READY state, partner state is PARTNER-DOWN
2022-04-28 22:43:06.415 INFO  [kea-dhcp4.ha-hooks/9787.140701841197248] HA_LEASE_UPDATES_DISABLED lease updates will not be sent to the partner while in READY state