the confg guide says to config. the devices in HA with Manual Confg Sync to test changes prior its replicated to the group.which makes sense,but,does that mean you have to always check & make sure you are always logged on to the Active unit before making a change?or it doesnt matter?
Determining the best way to manage configuration changes and syncing config is up to you and your site change management process.
Many people do make changes only on the Active device for the following reason:
If you make a change on the Active (with manual sync), and it goes catastrophically wrong (i.e a service is interrupted), then you can immediately fail-over to the standby device that does not have the change to restore service. You can then push the config from the working device to the non-working device to revert the change.
If you make a change on the Standby, you need to failover to test the change which may result in some level of outage.
If you make the change on the Standby, and then sync the config from the Standby to the Active, you no longer have the ability to fail-over to the original config. As both devices now have the same config, if the change causes an issue, you can only roll-back the change by restoring an Archive on one device and syncing.
I hope this helps.