看到 AWS 公告提供 CloudFront 的 origin subnet 資訊 (AWS-managed prefix list) 讓管理者可以用：「Amazon VPC now supports an AWS-managed prefix list for Amazon CloudFront」。
以往會自己去「AWS IP address ranges」這邊提供的 JSON 檔案定時撈出來再丟到 managed prefix list 裡面，這次的功能等於是 AWS 自己管理這個 prefix list 讓管理者使用。
馬上想的到的用途就是 HTTP/HTTPS port 了，只開放給 CloudFront 的伺服器存取：
Starting today, you can use the AWS managed prefix list for Amazon CloudFront to limit the inbound HTTP/HTTPS traffic to your origins from only the IP addresses that belong to CloudFront’s origin-facing servers. CloudFront keeps the managed prefix list up-to-date with the IP addresses of CloudFront’s origin-facing servers, so you no longer have to maintain a prefix list yourself.
要注意的是這不應該當作唯一的 ACL 手段，因為其他人也可以建立 CloudFront distribution 來穿透打進你的 origin server。
另外有個比較特別的地方，這個 prefix list 的權重很重，使用他會算 55 條 rule 的量，在 security group 內很容易撞到 60 條的限制，在 route table 裡面則是直接撞到 50 條的限制；不過這兩個限制都可以跟 AWS 申請調昇：
The Amazon CloudFront managed prefix list weight is unique in how it affects Amazon VPC quotas:
- It counts as 55 rules in a security group. The default quota is 60 rules, leaving room for only 5 additional rules in a security group. You can request a quota increase for this quota.
- It counts as 55 routes in a route table. The default quota is 50 routes, so you must request a quota increase before you can add the prefix list to a route table.
如果 HTTP 一條，HTTPS 也一條，那就會算 110 rules 了，有暴力的感覺...
