1. A method comprising: receiving configuration instructions for elements of a network topology to be simulated and tested; configuring via an Application Programming Interface (API), in response to receiving and in accordance with the configuration instructions, a plurality of software images running in a cloud host for a plurality of virtual network elements in the network topology, each of the plurality of virtual network elements having a custom driver; configuring via the API, in response to receiving and in accordance with the configuration instructions, the custom drivers of the plurality of virtual network elements with data representing one or more connections between the virtual network elements, the data representing the one or more connections including standard properties for a physical network element and custom properties for emulating behavior of a physical layer of the physical network element; generating test traffic for use in executing the plurality of software images for the plurality of virtual network elements in the network topology for purposes of testing the network topology; and executing the plurality of software images for the plurality of virtual network elements in accordance with the data representing the connections, for development and testing of the network topology.