Im guessing you are doing this offline you your pc and the controller and the AP just to test though....
But when you connect it ot the real Network you will have your APs on another vlan
Let say
You got your controller with vlan 800 with the ip you said 10.200.50.253
You got that vlan trunked to your switch core and then trunked that vlan 800 back and on the switch core an ip interface vlan which will be the default gateway of that Wireless controller... let say you will have an ip interface vlan with the ip 10.200.50.1 on the SwitchCORE
And your default gateway will be the CORE switch which is routing that vlan(for now thecontroller should be just a layer 2 at this momment which is recommended.
Now just with that you should have aministration on the network of the Wireless contorller.
Now the APs might not be on that vlan... they will be in X vlan...
So now you got the dilema that you need your APS can find the controller.
It can be done in many ways....
1-By statically configuring it
2-by DNS
3-by DHCP
4-with ADP protocol(which will find it if the AP is on the same vlan of the Wireless controller)
I llike the DNS one
On the DNS server you put a new record aruba-master which willl be 10.200.50.253
Now if you connect the AP on any vlan that has a DHCP server that distribute the DNS server ip on that dhcp scope he willl get the IP in X vlan and also but as he will resolve with the DNS server that the master is 10.200.50.253 he willl find the controller and you should see it ont he screen.
Hope this help you