Edit: I found this video https://www.youtube.com/watch?v=St3SE4LWhKo it uses the slides I mean but looks like there are a few versions from different events. Google for "another day, another billion packets"

I remember what it looks like, tried to Google it but can't find it. The gist of it was that they didn't create any tunnels or VPN like infrastructure to create VPC, because it wouldn't scale to large numbers of nodes. Especially because your servers can be on completely different hosts all of their internal network.