Answer:
Use an application container.
Explanation:
Host operating system is software installed in a computer that interacts virtually with a server and also describes the difference between its software and a guest operating system.
It interacts with the hardware and works with atype 2 hypervisor which does not interact with the hardware but create virtual machine interfaces for multiple guest operating system to be installed, which are not necessarily the same as the host os.
Host os can also be used to describe operating systems that make use of container based virtualization. Containers are storage partitions used to hold applications separately on the same server, instead of replicating the operating system.
So with a container, Josh can separate the legacy application from other applications in the server.