1. A method to provide fault tolerance in a virtualized computing environment with a first fault domain and a second fault domain, the method comprising: determining whether a primary virtualized computing instance and a secondary virtualized computing instance are both in the first fault domain, wherein the secondary virtualized computing instance is configured as a backup for the primary virtualized computing instance and supported by a first host; in response to determination that the primary virtualized computing instance and secondary virtualized computing instance are both in the first fault domain, selecting, from the second fault domain, a second host based on a resource availability of the second host; and migrating the secondary virtualized computing instance from the first host to the second host, thereby migrating the secondary virtualized computing instance from the first fault domain to the second fault domain.