HA architecture across subnets, MPE and APE & SQL AlwaysOn Cluster

I am doing some analysis on the architecture for a new environment, and HA is a requirement.

Currently we have licensing for NCM, SAM, IPAM, NTA, NPM

We also have a license for a additional polling engine (APE)

I know we would need to purchase a license for HA.

Thought it would be worth mentioning:

  • Make use of a 2017 SQL AlwaysOn Cluster.
    • SQL cluster will be HA between our two London data centers
  • The Main Polling Engine (MPE) will be located in London
  • The APE will be located in Vancouver.
    • Reason for the geographically dispersed polling engines is that the majority of our VM's are located in London and Vancouver.
  • Make use of Microsoft DNS for the virtual hostname

The questions i have are:

  1. In order to introduce HA will i need HA on both the MPE and APE?
    1. e.g. a third server that will act as a secondary server to the MPE and a fourth server that will act as the secondary server to the APE Orwill the APE become the HA pool member?
    2. e.g. two HA licenses / two HA pools (total of 4 Orion servers)

Below are the two options...which one is correct?

Anything i have missed?