Route 53 DNS queries when CNAME points to an A record

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My customer has significant number of requests trying to cost optimize.

In Route5 3 there is a CNAME xxx.yyy.com with TTL=300 pointing to zzz.yyy.com which is an A record with TTL=60 which points to IP. When clients on the web try to resolve xxx.yyy.com, will there be 2 DNS queries issued to Route 53 (adding two to billing) or there will be only one because route53 will follow CNAME at once? It’s also dependent on the client/ISP behavior and cache but what it will be 1 or 2 ?

They have thousands of such subdomains constantly being queried by millions of clients in certain geography, but each subdomain may be not as frequently queried as such short TTL. Increase of the TTL is not so good as they need to be able to quickly respond to unexpected change of IP.

I did tcpdump on port 53 from EC2 machine and I see only 1 request going out but I’m not sure if this is the right test.

asked 4 years ago25 views
1 Answer
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Accepted Answer

R53 doesn't "follow" anything; it is the resolver that will resolve the initial CNAME and the subsequent A record, leading to two charges should both records be hosted on Route 53.

Your customer should look into making use of Alias records wherever they can if this is a concern to them.

https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/resource-record-sets-choosing-alias-non-alias.html

answered 4 years ago

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