AWS is IPv4-only? Can you elaborate? It seems IPv6 is pretty well supported.

https://docs.aws.amazon.com/vpc/latest/userguide/get-started...

I wasn't implying it was IPv4 only, I was merely teasingly repeating rumors that a lot of low level infrastructure still has IPv4 assumptions that Amazon has had enough IPv4 addresses to date that they don't need fix those underlying assumptions in their data centers. It's mostly dumb rumor mongering, I suppose, as I'm not sure I have a citation for that off hand other than other HN jabs at Amazon/AWS. I'm sorry for that, it was an unnecessary jab/tease, that I will blame on pre-coffee brain.

They used to -- that's why IPv6 was so slow to arrive. But that's fixed now except possibly in some parts of "legacy EC2".

We have IPv4 and IPv6 public interfaces on our AWS services.

The people desperate to use IPv4 are not AWS themselves. AWS doesn't buy stuff just to have it. They buy it because customers are using it. AWS customers are moving stuff out of their data centres and don't know how to use serverless, load balancers, dynamic cloud capabilities (like spinning down instances when they aren't in use) and so on. Customers are doing lift-and-shift in vast volumes and they're doing it in the only way they know how.

This. A lot of those lifted apps will be legacy services built in 2000-2009 that must run 24/7 and only know about ipv4.

Why specifically -2009? What happened in 2010?

(I'm aware a lot of things happened in 2010, but (as someone interested in the industry but somewhat removed from it) I'm not aware of anything that specifically happened in 2010 that changed the landscape in a big way.)

AWS has heavy support for IPv4 because back-end stuff is all IPv4 and there isn't any push to change. IPv6 doesn't add any real value for servers that are all living in a private address space anyway, it adds an overhead to each packet, and learning off your addressing schemes is far easier with dotted quad.

IP isn’t supposed to have “private address space”. The only reason it does is because the address space is scarce. NAT does not make your network “private” or provide security, firewalls and good host software do that. NAT literally breaks IP.

RFC 1918 (Address Allocation for Private Internets) disagrees with you, and has done since at least 1996.

RFC 1918 describes space for entirely private networks, not “private extensions” to the public globally routable internet. There’s a subtle but important difference. The private addresses strictly aren’t routable on the public internet. NAT (which there’s also an RFC for) is what what allows packets to flow between private disjoint IP networks. IP is only scoped to work within a single network, whether it’s public or private or triangle.

That screws up when two private entities merge and discover that they're using the same RFC1918 block.

(or just want to interoperate, even)

End-to-end principle disagrees with you. As does my network. All routable IP space baby. Makes things a breeze.

IPv6 got a private address space, even if we shouldn't run out of IPv6 addresses anytime soon.