I have a quaestion about a new AP association to secondary WLC.
So, I have two offices, one of them are 18 AP and one WLC and the second office is two WLC and 10 AP's.
THE WLC have the same software version installed.
Suppose that all is configured well.
The scenario is that the WLC from first site failed and all AP's are beginning association to WLC in the seconde site.
In this reason the AP starts donwloading a image from the WLC in the second site?
The failover process is described below
Power down the primary controller to which the AP is currently registered. The AP waits for the heartbeat time set, which is 30 seconds by default, to detect the failure of the primary WLC. After this period of time, the AP sends heartbeat messages seven more times, one per second, in efforts to find the primary WLC. If the AP does not hear from the primary WLC, the AP registers to an available WLC via the default process. Therefore, the process to detect the primary WLC failure and register to the secondary WLC takes approximately 80 seconds. Once the access point joins the secondary controller, it continues to send the discovery request to the primary controller in order to determine if the primary controller is back in operation. This can be determined with the help of the debug lwapp client packet command.
Note: The heartbeat message is similar to a keepalive message. The AP heartbeat is set to 30 seconds by default. You can adjust this heartbeat time, down to 1 second. However, if you have not made this adjustment since the last time that the AP heard from the WLC, 30 seconds pass before the AP realizes that it cannot reach the WLC.
If a WLC goes down, all the APs that are registered to that WLC automatically switch to the other WLCs in the mobility group. When the primary controller comes back on, the APs fall back to it. However, this operation takes 30 seconds. During this period of time, the service to the APs is interrupted as the APs rejoin the primary WLC.
From this excellent doc;
The AP only needs to download a new image if the new controller has a different code version. Since you said your controllers were running the same version, your APs would not need to load a new firmware when they are pushed to the second controller.