|Question||How does license server failover work in AOS version 6.3?|
|Environment||This article applies to all the controllers running AOS version 18.104.22.168 or above|
If the license server goes down, the standby license server will take over as the license server. It will continue to send license information to the license clients. If the controller acting as a standby license server is unable to reach the license server, it will retain the license limits that it obtained from the server initially till a reboot. In other words, the backup license server will have access to all the licenses that were being served by the master till the backup server reboots.
If the license server goes down and there is no standby license server, no license limits can be sent to License Client controllers that are starting up while the license server is down. Existing controllers that had license limits sent to them will continue to function as normal for 30 days. When a license server is unable to reach a license client for 30 days, the licenses that were imported from it will be removed from the license database of the server.
A warning message will be displayed on login when the license client cannot reach the server and its limits received from the server are about to expire. A similar warning message will be displayed on the license server when it cannot reach the license client and the limits received from the client are about to expire.
During failover from one controller to another, we have protection in place to prevent outages. If an AP fails over from one client controller to another, the AP will be allowed to come up even if there aren’t sufficient licenses present. This is to ensure that redundancy is not broken. If the AP reboots after failing over it will only be allowed to come up if sufficient licenses are no present. In a failover scenario, it is expected that the licenses from the controller that went down will be returned to the main pool by this time, so a license will be available for the rebooted AP.
If the license server has not received 3 consecutive heartbeats (90 seconds) from a client, it will add the client's used license limits to the available limits. If the client has not received 3 consecutive heartbeats (90 seconds) from the server, it will add the server’s used license limits to the available limits. The default heartbeat interval is 30 seconds. This is to ensure that the licenses are redistributed in case of a failover.
Following command show the last heartbeat exchanged between the license server and the license client:
(Master-1) #show license heartbeat stats
License Heartbeat Table
Client IP Address HB Req HB Resp Total Missed Last Update (secs. ago)
----------------- ------ ------- ------------ -----------------------
172.16.0.253 498 498 0 5
172.16.0.254 499 499 0 5