CNAME Records vs R53 Alias Records

Ref: https://learn.cantrill.io/courses/1820301/lectures/41301581

Limitations of CNAME Records

💡 Refresher: CNAME records map hostname to hostname
- e.g. www.catagram.io → catagram.io
👎 Limitation of CNAME records: can NOT map the domain apex (i.e. the naked domain)!!
- e.g. catagram.io → www.animals4life.org is NOT valid with CNAME records!
- DNS standard does not support this functionality
- Many AWS services (e.g. ELBs) grant access via a DNS name, not an IP address
  - www.catagram.io → ELB is valid with CNAME records…
  - ‼️…but catagram.io → ELB is invalid!!
- R53 Alias records overcome this limitation

🔧 AWS-exclusive record outside of the DNS standard
- Main function: Map hostname to an AWS resource
  - For non-apex/non-naked names → functions like CNAME
  - ❗ Allows apex/naked domain to be mapped, unlike CNAME!
- ‼️ Can only be used if R53 is hosting your domains!
Actually a subtype of normal DNS records
- e.g. A-ALIAS, TXT-ALIAS…
- Determine type of R53 Alias record by matching it to what the AWS resource returns
  - e.g. ELB returns an A record → create an A-ALIAS record pointing at the DNS name provided by the ELB
Can point to services like APIGW, CloudFront, Elastic Beanstalk, ELB, Global Accelerator, S3…
‼️ No charge for ALIAS requests pointing at AWS resources!
- AWS encourage you to use ALIAS records
- 💡 For anything pointing to an AWS resource, default to picking ALIAS records