Techniques disclosed herein relate to migrating virtual computing instances such as virtual machines (VMs). In one embodiment, VMs are migrated across different virtual infrastructure platforms by, among other things, translating between resource models used by virtual infrastructure managers (VIMs) that manage the different virtual infrastructure platforms. VM migrations may also be validated prior to being performed, including based on resource policies that define what is and/or is not allowed to migrate, thereby providing compliance and controls for borderless data centers. In addition, an agent-based technique may be used to migrate VMs and physical servers to virtual infrastructure, without requiring access to an underlying hypervisor layer.