multi subnet HA

DNS is used in HA solely as a convenience feature for those customers running HA in a multi-subnet failover configuration who need some mechanism for redirecting end-users to the active member hosting the Orion web interface but do not have a load balancer. 

DNS can also be used by some devices to send Syslog, SNMP Traps, or Flow to a poller in a multi-subnet failover configuration, also in the event a load balancer is unavailable. 

Long story short. If you have your own solution for directing incoming traffic to the active Orion server, then there's really no need to configure Orion HA to update DNS records. 

Thanks for the explanation. for Traps etc, i will keep both primary and secodnary IP address on the nodes.

if i have Additional Polling engine, will the regular communication between them be initiated from MP or APE also initiates some services?

for NCM, i will be in trouble and i will have to forget HA for NCM but i am worried about NPM .

if i have Additional Polling engine, will the regular communication between them be initiated from MP or APE also initiates some services?

Additional Pollers require bi-directional communication with the main poller and main poller backup. This means the APE can initiate the communication to the main poller, or the main poller can initiate communication with the APE. This is communication is done using the actual hostname of each machine and not the optional DNS name entered during the High Availability pool setup wizard, regardless if HA is used or not.

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for NCM, i will be in trouble and i will have to forget HA for NCM but i am worried about NPM .

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Why will you need to forget about HA for NCM? 

Thanks about the APE communication. this means, i can use hostfile in the APE for both primary and secondary and i dont have to worry about DNS.

regarding NCM, for example binary config backup, i will have to define the IP address of config storage device. since its a single IP address, i cant use HA and will have to point it to a single server.

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.regarding NCM, for example binary config backup, i will have to define the IP address of config storage device. since its a single IP address, i cant use HA and will have to point it to a single server.

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There are a variety of different high availability options available for making NCM's binary storage redundant. The most popular option that many customers use is DFS. It's native to the Windows operating system.

https://docs.microsoft.com/en-us/windows-server/storage/dfs-replication/dfsr-overview

Thank you so much.  i will explore and test them.

Thanks for your time again.