I recently read a very interesting post on LinkedIn in which Urs Hölzle, one of the original Google network engineers, celebrated twenty years of Google network innovation. He provided links to the recent paper from Google describing how Google developed its datacentre network and how it has evolved since then. The paper describes how Google applied the Clos network topology in its datacentres and the early implementations of software-defined-networking that controlled data flows across the network.
One point that was really interesting, which came up in the comments to the article, is that Google implemented the original network routing code in Python.
Mr. Hölzle also linked to an independant research report that came out at the time. It provided the initial view of what Google was developing and is interesting to read almost 20 years after it was written.