A regional API endpoint is a new type of endpoint that is accessed from the same AWS region in which your REST API is deployed. This helps you reduce request latency when API requests originate from the same region as your REST API.
The nine new Regional Edge Cache locations are in Northern Virginia, Oregon, São Paulo, Frankfurt, Singapore, Seoul, Tokyo, Mumbai, and Sydney.
edge 會先到這幾個 regional edge 再到 origin：
These locations sit between your origin webserver and the 68 global edge locations that serve traffic directly to your viewers.
然後預設都開啟了，沒有額外費用：
Regional Edge Caches are turned on by default for your CloudFront distributions; you do not need to make any changes to your distributions to take advantage of this feature. There are also no additional charges to use this feature.
Most routers now do a per-flow load balancing, meaning packets on a TCP connection are always sent over the same path, but even a small percentage of routers with per-packet load balancing can cause the website to be unreachable for users behind that router.
所以 LinkedIn 的人試著測試 TCP Anycast 技術的穩定性：
So, to validate the assumption that TCP over anycast in the modern internet is no longer a problem, we ran a few synthetic tests.
測試的方式是設定 web server，讓下載速度不快，然後設了好幾個點並且放出對應的 routing，用 Catchpoint 服務監控，如果不穩定的話，應該就會收到 RST 中斷連線：
We configured our U.S. PoPs to announce an anycast IP address and then configured multiple agents in Catchpoint, a synthetic monitoring service, to download an object from that IP address. Our web servers were configured to deliberately send the response back slowly, taking over a minute for the complete data transfer. If the internet was unstable for TCP over anycast, we would observe continuous or intermittent failures when downloading the object. We would also observe TCP RSTs at the PoPs.
而好消息是，測試起來相當穩定：
But even after running these tests for a week, we did not notice any substantial instability problems! This gave us confidence to proceed further.
