A couple of things I learnt working with IAPs (and might be useful for people who haven't used IAPs before):
If all the Instant access points are running the same InstantOS version, are in the same VLAN and auto joining has not be disabled then the following occurs:
- An election for a master occurs. The Instant access point that wins the election takes on the duties of a wireless LAN controller. The Instant solution is called "controllerless" as a separate wireless LAN controller is not required but Javier is correct that Instant is not truely controllerless. The master acts as the (virtual) wireless LAN controller for its cluster (Instant access points in the same VLAN) so if you have multiple sites with unique VLANs I am assuming you will have multiple Instant clusters.
- The IAPs that are not elected the master synchronise their configurations with the master of their Instant cluster.
To access the Instant cluster you access the previously defined VIP and that automatically accesses the virtual controller. In the event that the current virtual controller goes offline another election occurs and the new virtual controller takes over. The Instant cluster can still be accessed using the same VIP. So if you had three IAPs you need four IP addresses - one static for the VIP and three DHCP/static for the IAPs. The VIP is defined in the IAP's configuration.
Therefore, you don't need Aruba Central to manage a small Instant deployment (just access the Instant cluster's VIP with a web browser) but if you have a number of Instant deployments (maybe offices in different cities) it allows you to monitor and manage your IAPs.
A new version of Aruba Central is expected late this year/early next year that will include a "highly configurable" external captive portal option. This is important as the Instant internal captive portal does not resize due to the wireless client's screen size so is and issue with smartphones and other small screen devices.