Juniper WLC Licensing + Cluster - Update

So Juniper wireless licensing as I know it has changed! Previous I thought it was the same as Cisco where you had to have enough licenses per controller to handle all APs should a single controller fail but this is no longer the case.

The way that AP licensing now works on Juniper WLC is that WLC can burst up to double their current installed license count as long as they have installed the HA license: WLCXXX-HA-RTU

Therefore if you have 100 APs, each WLC can have 50APs licensed and the HA license, this allows up to 100 APs in the event of a single AP failure.

One note on this is that you do not require the HA-RTU license in order to cluster Juniper WLCs. The only thing that the HA-RTU license grants you is the ability to burst to double the installed license capacity. Clustering is configurable without it, but each WLC will be limited to the number of AP licenses is currently has installed.

Here is a great description of Juniper WLC Clustering I was given:
A cluster is something you create inside a mobility domain which enhances the reliability and redundancy features in a mobility domain. A mobility domain does provide controller redundancy but an AP needs to reboot in order to find the redundant controller. If you enable A/A clustering it provides stateful peering between controllers therefore the APs do not need to reboot during controller failure. This is a powerful feature specific to Juniper which clients like for ISSU and unplanned outages. A mobility domain supports up to 64 WLCs from which a maximum of 32 can participate in a A/A cluster (currently max size of a cluster is 4096 APs) . Clustering provides the following benefits:

o   Hitless Failover (AP switches to secondary AP manager subsecond)

o   Hitless software failover

o   AP load balancing (automatic balancing of all APs across all clustered WLCs in your mobility domain)

o   Cluster configuration - you define your complete wireless configuration once on the seed

Juniper Clustering is great because of the truly hitless failover, the WLC are configured in a A/A cluster and when controllers are clustered each AP maintains connectivity with it's Primary AP Manager (PAM) and Secondary AP Manager (SAM), the PAM propagates client sessions to the SAM. For voice, once a call is setup, local switching would occur to avoid any issues with latency caused by tromboning traffic via a controller. Data can also be locally switched which is great because you can choose how extensively you want to implement local switching choosing when to use either local or central switching. An AP failure is not even considered as 'system failure’, it is seen as a roaming event. The nearby AP taking over the session will not distinguish between ‘nearby AP failure’ or ‘user approaching AP with better signal strength’.

ISSU works in a similar fashion when running a virtual controller cluster. APs without sessions are targeted first and those with sessions take neighbouring APs into consideration allowing session roaming to neighbours before updating the now session free AP.