Beyond using overlay networks from the hypervisor and doing things like load balancing in software with a bit of extra special sauce, there isn't really as much

Beyond using overlay networks from the hypervisor and doing things like load balancing in software with a bit of extra special sauce, there isn't really as much "software defined networking" going on in these places. Certainly no magic as articles like this make out. In the underlay it's all still very much basic, old fashioned networking using existing protocols: BGP in the DC at FB and MSFT, and BGP, ISIS, MPLS in the WANs. (AMZN likes to pretend they're special so I won't comment on them.) Google is a bit different, in part I think this is due to their culture and early scale they were forced to drive a lot of developments wrt merchant silicon use, and this naturally led them to their own network OS solutions, with a simplified semi-centralized IGP solution for their DCs, and centralized-TE solution for their inter-DC WAN. It's not entirely clear to me if they would still feel the need to do this if they were starting again.