Postgresql['vip'] configuration of Chef HA

Hi Chef users,

I just built my Chef HA cluster and I am a little concerned about the following configuration in chef-server.rb of my Frontend server.

postgresql['external'] = true
postgresql['vip'] = ''
postgresql['db_superuser'] = 'chef_pgsql'
postgresql['db_superuser_password'] = '****'

The /etc/opscode/chef-server.rb was generated by the way mentioned in the manual

My question is: do I need to create a VIP for my 3-node backend cluster and replace postgresql['vip'] = '' with postgresql['vip'] = '<vip_of_backend>' ?
As it seems that it is not required to change the default vip value as per the manual mentioned above.
And everything (uploading cookbook etc,.) seemed to work well when I keep the default .