I'm using CloudFront to distribute my static website and I've set up Edge locations in various key global areas. I'm a bit confused about how the DNS lookup process works when a user enters my web address. How does it determine the best Edge location for that user? If anyone could clarify this for me or point me to some helpful resources, I would really appreciate it!
4 Answers
CloudFront uses Anycast IPs to automatically direct traffic to the nearest Edge location based on various factors like load and latency. Essentially, the DNS returns these Anycast IPs to guide users to the optimal server. Keep in mind though, that standard CloudFront doesn’t use Anycast without an additional cost.
Check out this resource: [Anycast](https://www.cloudflare.com/learning/dns/what-is-anycast-dns/). It gives a solid overview of how DNS routing works and how it relates to CloudFront.
CloudFront leverages custom resolver logic to find the best IP address based on your location. When a DNS request comes in, it checks any available EDNS0 extended fields or estimates the client's location from the DNS resolver. It selects the optimal Point of Presence (POP) considering your location, ISP, load, and current traffic to balance performance and cache efficiency.
DNS lookup for CloudFront is managed using EDNS0 with a feature called Client Subnet. This allows your DNS server to share part of your IP information with upstream DNS providers (like Route 53). Based on this info, the DNS server can route you to the nearest Edge location.
Actually, standard CloudFront doesn’t include Anycast; that's an extra $3,000 per month option if you want that feature.