Anycast is just advertising the same route out of multiple locations, it's an old trick for faster DNS response and for CDNs with static content and was in use long before it got the name Anycast.

For a dynamic service like T_D that operates on a single database, anycast can just not work. You would need to lock and synchronize the databases for every write from every location. It's impossible to maintain state without a huge impractical overhead that would make things unusable.

This why even places like Reddit handle their platform with load balancers on the front end and a huge database cluster.

I used to work for Cisco, I have done a huge amount of networking and worked on ios for them, I know what I am talking about my pede.

I get the feeling you actually don't know how Anycast works, it's just advertising the same route from different locations, nothing more. I'll explain.

Say I have a site in San Fran and I have a server 8.8.8.8, I advertise to my BGP peers 8.8.8.0/24. So there exists a single route to that server in the global routing table. Now people in Australia are using my server but complain it is too slow, so I add a new server with the same content and same IP address in Australia and I also advertise 8.8.8.0/24 from my Australian site to my BGP peers there.

So what happens? The global routing table ends up with two destinations to 8.8.8.8, what's the next hop? The route with the lowest cost. So Routers closer to Australia will pick the path to the Australian 8.8.8.8 server and those closest to San Fran will pick the path to the San Fran server. If one of those sites has a power outage, then I also get fail over automatically to the next closest server. I can keep adding locations and 8.8.8.8 servers all over the world if I like.

That's it, that's Anycast. It should now be clear why that can only work with sites or data that is static or gets updated very infrequently. It should be obvious that something like a dynamically built forum with hundreds of writes per minutes isn't suitable for Anycast. It is very common for reverse proxies to be on anycast addresses, this is what has people confused, as a reverse proxy just sends traffic to the real server.

You are right, IPv6 was meant to solve the address depletion issue but it is extremely hard to get people to move to it. IPv4 is just what everyone knows and understands so they are trying to cling to it as long as they can. The main reason is addressing.

An IPv4 address looks like this 192.168.45.10, I guess you know that. An IPv6 address looks like this: 2607:f0d0:1002:0051:0000:0000:0000:0004

I can be shorted so the zeros are removed but it still looks like this:

2607:f0d0:1002:51::4

Then there is the problem of interconnecting Ipv4 to IPv6 networks, IPv6 is not backward compatible with IPv4 so you need to translate between the two and run both stacks on every router.

So people have spent effort in to delaying it, for example many mobile carriers run NAT between the mobile network and the Internet. If they didn't we would have been out of IPv4 addresses years ago because of smart phones.

So has anything happened in the last 10 years? Kind of, service providers are almost all running IPv6 in their core networks and many will give out IPv6 addresses on request but you generally need to ask for it. In the corporate world, mostly the same as things were 10 years ago, it's seen as an unnecessary change and I doubt many will even bother.

Yeah, IPv6 is basically free. The trouble is adoption is still not that great. I think all major wireless carriers use it now for mobile devices, so that should be good enough for most of us.

The problem was the size of the global routing table, it got to the stage where the mid tier carrier class routers were getting close to running out of memory even when upgraded to max memory. So carriers refused to accept anything that wasn't summarized to at least a /19.

Likely changed now, those routers should be long retired by now.