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: arranging virtual nodes in the network in a descending order of a total number of required resources; mapping the virtual nodes over physical nodes while balancing a load for different types of resources; arranging virtual links in a descending order of estimated spectral resources; mapping virtual links over physical routes and selecting a modulation format for the virtual links while balancing the load over physical links; and assigning wavelength and spectrum to the virtual links.