A computer system includes hosts for hosting virtual infrastructures. Compute resources provided by the hosts are allocated to user groups (e.g., departments, projects) in the form of reservations that define amounts of resources available to the user groups. Tags can be associated with both hosts and with reservations. A reservation has access to resources of a host having a host tag that matches a user tag associated with the reservation. Thus, to make a host available to a reservation, either 1) a tag can be added to the reservation to match a tag of the host, or 2) a tag can be added to the host to match a tag of a reservation. This can be more convenient than a case in which both a host and a reservation must be configured to give the reservation access to the host.