Abstract: The number of compute resource required by a user in a computing environment may change dynamically. For example, the virtual machine instances allocated to a particular user may host a web service. As queries to the web service increase, the current number of allocated virtual machine instances may be insufficient to provide timely responses. In response to the increased demand, the computing environment may increase the number of instances allocated to the user. To do so, the computing environment maintains one or more already executing virtual machine instances in a hotpool that have not been assigned to any user. When a user needs additional computing resources, one or more of the virtual machine instances in the hotpool may be allocated to the users. Because these instances are already executing, the computing environment avoids the relatively long delay corresponding to generating a new virtual machine instance.