F5 as high availability failover and not as load sharing?

Edit: I have problems to implement it, I followed the guide:

1. Made a virtual server.

2. Created a pool with the real servers in it.

3. Created an iRule "single_node_persistence" like this:

     
     when CLIENT_ACCEPTED { persist uie 1 }    
   

4. Created a Persistence profile "single_node" of type Universal which uses the iRule I just created and et the timeout 360 s.

5. In the virtual server definition, applied pool as the default pool, and tried to apply new persistence profile "single_node" as the default persistence profile, but got error:

01070585:3: Virtual server (test_pool) cannot reference rule (single_node_persistence) more than once (check persistence, auth and rules).

What did I miss?

Or shall I leave the default settings:

Default Persistence Profile None

Fallback Persistence Profile None