I ran network team at an organization with hundreds of thousands hardware hosts in tens-of-megawatts large data centers, millions of VMs and containers, links b

I ran network team at an organization with hundreds of thousands hardware hosts in tens-of-megawatts large data centers, millions of VMs and containers, links between data centers, links to ISPs and IXes. We ran out of RFC1918 addresses at around 2011-2012 and went IPv6-only. IPv4 is delivered as a service to nodes requiring it via an overlay network. We intentionally simplified network design by doing so. This is neither hard nor expensive.