Proactive HA is a very cool new feature that was introduced in vSphere 6.5, which enables our hardware vendors to communicate their hardware specific health information directly into vSphere and specifically with vSphere DRS. This hardware health information can then be leveraged by vSphere DRS to take proactive actions to guard against potential hardware failures. Brian Graf, Product Manager for Proactive HA, DRS and overall vSphere Availability has a nice blog post here where he goes into more details on how Proactive HA works.
As Brian mentioned, a few of our select hardware vendors are already in the process of developing and certifying Proactive HA integrations for vSphere, so stay tuned for those announcements in the future by both VMware and our partners. In the meantime, there was an interesting comment from one of our field folks asking whether it would be possible to "simulate" the new Quarantine Mode operation for an ESXi host to be better understand how this feature might work?
Quarantine Mode is new mode for ESXi, which can only be triggered by Proactive HA. It functions similar to the Maintenance Mode operation, but instead of migrating all VMs off, it will allow existing VMs to continue to run but prevent additional new VMs to be placed on the host.
Proactive HA does provide a set of public vSphere APIs under the healthUpdateManager which is primarily targeted at our hardware vendors to consume. However, these APIs could also be used by our customers to get visibility into the current Proactive HA configuration as well as the health of the ESXi hosts from the Proactive HA provider standpoint. Going back to our initial question, it is possible to "register" a fake Proactive HA provider and manually generate health updates to simulate what a real Proactive HA solution could look like.
Disclaimer: This is for educational and lab purposes only. Creating a fake or simulated Proactive HA provider is not officially supported by VMware, please use at your own risk. The creation of Proactive HA providers as well as publishing health updates is for our hardware vendors to consume which in turn will provide native integrations that include customer visible interfaces within the vSphere Web Client.