Aspects of the present disclosure relate to flexible and automatic provisioning of virtual instances in a virtual network using single-root input/output virtualization. A device pool is defined that is associated with a virtual entity, such as a virtual switch, in a data center. The device pool identifies available physical hardware devices of one or more host machines, such physical network interfaces connected to the virtual switch, and the device pool is associated with the virtual entity. When a virtual computing instance is connected to the virtual entity, such as when initialized or after migrating between hosts, one or more physical hardware devices are automatically assigned from the device pool to the virtual computing instance based on the association of the device pool to the connected virtual entity. Thus, VMs can be flexibly and automatically provisioned with SR-IOV physical hardware when migrating between hosts using SR-IOV.