APIC standby controller operational status is unregistered

[ThinMan]

Hello, I have just added a standby controller (apic version 6) to a 3 node active apic cluster. under the standby controllers section, I can see everything seems okay, when going into the node 21, I see the operational state of the standby controller is  unregistered. and also the status for show controller via CLI, the status is "online" for the standby controller.  also went into the options to "accept controller" but there are no changes. 

There arent much documentation/guide from Cisco for Standby controllers. Could someone please help me with the below ? 

1.  is this the expected state for standby controllers ? 
2. are there anything else I can run/do to verify the status of the standby controller, or to make sure the database on the standby is in synch ?
3. also, as per cisco's guide, once the standby is registered, you can only access via SSH option and can only login via "rescue-user" but I can still access https. please confirm ?

see attached outputs.

[AshSe]

As you know a cluster size of 3. 5, or 7 is recommended. An APIC cluster with 4 or 6 APICs is not recommended. 

Take a glimpse of Cisco APIC v6.0 "Getting Started Guide"

Cisco APIC Getting Started Guide, Release 6.0(x) 

Please confirm that you are able to see similar topology under System > Controllers > Topology

from your details; it looks your setup is correct.

[ThinMan]

thank you but just to make myself clear, I am adding a “standby controller” to a 3 node cluster not expanding the active cluster.

[AshSe]

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There arent much documentation/guide from Cisco for Standby controllers. Could someone please help me with the below ? 

1.  is this the expected state for standby controllers ?  >>> Yes, same I can see in my setup
2. are there anything else I can run/do to verify the status of the standby controller, or to make sure the database on the standby is in synch ? >>> No, you are good at this state.
3. also, as per cisco's guide, once the standby is registered, you can only access via SSH option and can only login via "rescue-user" but I can still access https. please confirm ?  >>> Yes, you get the https login window and prompt to enter but since APIC-4 is not yet synced you will not be able to login. The only way to login is rescue-user, password for which is generated by Cisco Tac only.

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This document: Configure Standby APIC though is written for older version (IMO v2.0) but still can give you a fair idea of configuring a standby APIC.

Last but not the least, response to your query #2, and #3 as per above document:

• Cisco recommends standby APICs in the same POD as the active APICs it can replace. No data is replicated to standby unit, not even admin credentials (Rescue-user log in works ).

PFA, APIC-4 https, login attempt screenshot

HTH

Please Accept the Solution if it addresses your query.