1. A system for the migration of virtual machine instances in a virtual network, comprising: a computer system including a processor executing software code to implement a migration management service operable to: monitor a resource metrics of hosted virtual machine instances, wherein the hosted virtual machine instances correspond to hosted database functionality; determine, based on the monitored resource metrics of the virtual machine instances, a set of one or more target hosted virtual machine instances for migration; prioritize, based on additional information, the set of one or more target hosted virtual machine instances by: determining a minimum service level associated with each of the hosted virtual machine instances, determining whether a first hosted virtual machine instance is causing another hosted virtual machine instance to violate the minimum service level associated with the another hosted virtual machine instance, and prioritizing the set of one or more target hosted virtual machine instances at least partially on the determination of whether a first hosted virtual machine instance is causing another hosted virtual machine instance to violate the minimum service level associated with the another hosted virtual machine instance; and cause at least a portion of data associated with one virtual machine instance to be migrated according to the prioritized set of one or more target hosted virtual machine instances.