Which pools can enable autoscale given the following configurations: HostPool1 (1 host), HostPool2 (2 hosts), HostPool3 (3 hosts)?

The capability to enable autoscale in Azure Virtual Desktop is influenced by the number of virtual machines (VMs) configured within a host pool. Autoscale functionality is typically designed to manage scaling based on user demand and resource utilization.

In this case, HostPool1, with only one host, does not meet the requirements for autoscaling. Autoscale relies on having a minimum number of hosts to effectively manage load balancing and resource availability. Having just one host would make it impossible to scale down during low demand, as there wouldn't be any other hosts to take over the user sessions.

HostPool2, with two hosts, and HostPool3, with three hosts, both have enough VMs to support autoscaling. With two hosts, the system can easily scale down to one host when demand is low, and it can also scale up as necessary when demand increases. HostPool3, having three hosts, offers additional flexibility for autoscaling, allowing it to scale down to two hosts or even one if necessary while still maintaining availability.

Thus, the most appropriate choice is that only HostPool2 and HostPool3 can enable autoscale, as they have the requisite multiple hosts to utilize this feature effectively.