> where DNS is used to control which datacenters customer traffic is going to
That was never reliable in the first place because of caching and non-compliant DNS servers, but:
EDNS has a DNS protocol extension that will send your IP subnet to the authoritative host even if the request has gone through various resolvers.
Not all DNS servers implement this (notably, Cloudflare doesn't). You can easily check if your DNS server sends your subnet along DNS requests: try to open https://archive.today/. If you see a Cloudflare error or a connection refused/500 error, this EDNS feature is not supported. archive.* intentionally sabotages DNS responses for servers that don't carry these extensions.
BGP anycast would be a solution that can route customer traffic to local datacenters without needing to fall back to DNS hacks and the many broken DNS intermediates.
That was never reliable in the first place because of caching and non-compliant DNS servers, but:
EDNS has a DNS protocol extension that will send your IP subnet to the authoritative host even if the request has gone through various resolvers.
Not all DNS servers implement this (notably, Cloudflare doesn't). You can easily check if your DNS server sends your subnet along DNS requests: try to open https://archive.today/. If you see a Cloudflare error or a connection refused/500 error, this EDNS feature is not supported. archive.* intentionally sabotages DNS responses for servers that don't carry these extensions.
BGP anycast would be a solution that can route customer traffic to local datacenters without needing to fall back to DNS hacks and the many broken DNS intermediates.