vCenter High Availability is a new feature of vSphere 6.5. It only works with the linux vCenter. By the time you are done, you end up with an active, a passive and a witness nodes. In 6.5 there is an RTO of about 5 minutes; which varies depending on loads and hardware. File level replication is done through Linux rsync. Native postgres replication handles VCdb and VUMdb replication. SSH needs to be enabled on the vCenter prior to implementing vCenter HA.
Here is the idea illustrated:
Here are the configuration steps:
Step 1: Create a vCenter Server and a separate PSC. This is a must; they can't be one vm.
Step 2: Select your vCenter, go to Configure and select vCenter HA.
Step 3: Click on Configure on the upper right corner.
Step 4: Select the heartbeat ip address for the active vCenter.
Step 5: Specify the ip addresses of the backup vCenter and the heartbeat vCenter.
Step 6: Review the information and click on next.
Step 7: Click on Finish and wait.
Step 8: Monitor the recent tasks. This deployment will take a while.
Step 9: Verify the settings of the backup vCenter appliance.