At Microsoft Ignite 2018, I was able to attend the "What’s new in System Center Configuration Manager" session.

During that session, they introduced High Availability (HA) with the Primary Site Server. Starting in ConfigMgr 1806 you will be able to install an additional Site server that will be in passive mode. You can fail over to the Passive Site Server if means that if something happens to your Primary Site Server that is considered Active, you will be able to fail over to the Passive Site Server. You will need to plan for this during your implementation of ConfigMgr 1806. A passive Primary Site Server is only supported in a Standalone Primary environment.

Here are some noteworthy considerations when considering a passive Site Server:

  • Uses the same site database as your site server in active mode.
  • Doesn't write data to the site database when it's in passive mode.
  • Uses the same content library as your site server in active mode.

Another important note is that if you need to promote your passive Site server you must do so manually through the ConfigMgr console.
The question now is what do I need to do if I am using 1E Nomad and 1E PXE Everywhere? It’s simple. Install the NomadAdminUI extensions, NomadbranchTools, 1E Task Sequence Tools (App Migration).  Then the 1EBIOStoUEFI tools (if using) on your passive Site Server.
If you have PXE Everywhere installed on the Primary Site server and you plan to implement HA for ConfigMgr, I would recommend moving the PXE Everywhere Central installation to another server. Otherwise, you need to install PXE Everywhere Central onto the passive Primary Site Server. Then use a DNS Alias for the PXE Everywhere URL.  Lastly, you will make the switch in DNS when you need to promote the passive server.
You will also have to use a ConfigMgr configuration Item to change the PXE Everywhere URL on your workstations to the new DNS Alias.