1. A method comprising the steps of: implementing by a computer a cloud service embedding in a software defined flexible grid optical transport network, the implementing comprising: mapping working and backup virtual nodes over physical nodes; mapping working and backup virtual links over physical routes which comprises: finding two pairs of node-disjoint routes using a disjoint pair procedure on an auxiliary graph; selecting a maximum number of virtual links whose node-disjoint routes are partitioned into two separate groups; allocating spectrum at lowest available wavelength on a selected physical route for a virtual link; and finding two pairs of node-disjoint routes using the disjoint pair procedure while modifying the auxiliary graph.