1. A method comprising the steps of: implementing by a computer an embedding of cloud demands over a software defined flexible grid optical transport network, the implementing comprising: initially mapping virtual links over physical links in the network; finding potential modulation formats and routing solutions for a virtual link mapping; selecting a modulation format and a physical routing solution for a virtual link based on a probability of mapping the virtual link over the route using the modulation format; assigning a wavelength and allocation spectrum to a virtual link such that spectral fragmentation is minimized thereby improving likelihood of mapping virtual links over physical routes; and mapping virtual nodes over physical nodes which includes assigning virtual nodes associated with the mapped virtual link to the end of physical nodes of a selected route on which the virtual link is mapped; wherein the step of assigning a wavelength comprises finding a lowest wavelength slot starting from which consecutive wavelength slots are available and provisioning the virtual link VL at found wavelength slots on a selected route between physical nodes PNs.