Nguyễn Khánk's Wiki

# DNS Records

# Record types

  • How you want to route traffic for a domain
  • Each record contains:
    • Domain/subdomain Name – e.g., example.com
    • Record Type – e.g., A or AAAA
    • Value – e.g., 12.34.56.78
    • Routing Policy – how Route 53 responds to queries
    • TTL – amount of time the record cached at DNS Resolvers
  • Route 53 supports the following DNS record types:
    • (must know) A / AAAA / CNAME / NS
    • (advanced) CAA / DS / MX / NAPTR / PTR / SOA / TXT / SPF / SRV
Record Type Description Example (for example.com)
A Maps a domain to an IPv4 address. example.com → 93.184.216.34
AAAA Maps a domain to an IPv6 address. example.com → 2001:0db8:85a3:0000:0000:8a2e:0370:7334
CNAME Creates an alias from one domain to another. www.example.com → example.com
MX Specifies the mail server for a domain. example.com → mail.example.com (with a priority number)
TXT Stores text-based data, often for security. example.com → v=spf1 include:_spf.google.com ~all (an SPF record)
NS Lists the authoritative name servers for a domain. example.com → ns1.example-dns.net
SOA Holds administrative info for a DNS zone. example.com (contains info like the primary nameserver and administrator's email)
PTR Performs a reverse DNS lookup, mapping an IP address back to a domain name. 93.184.216.34 → example.com

# Common CNAME Examples

Record Name Record Type Value/Target Purpose
www.example.com CNAME example.com Redirects the "www" version of a site to the root domain.
blog.example.com CNAME blogs-provider.com Points a subdomain to an external service like a blog hosting platform.
shop.example.com CNAME store.shopify.com Directs a subdomain to an e-commerce platform.
ghs.googlehosted.com CNAME example.com Used to verify domain ownership with Google services.
cdn.example.com CNAME cdnprovider.net Routes traffic to a Content Delivery Network (CDN) for faster content loading.
old-domain.com CNAME new-domain.com Redirects visitors from an old domain to a new one during a migration.

# Aws notes

# Records TTL (Time To Live)

  • High TTL – e.g., 24 hr
    • Less traffic on Route 53
    • Possibly outdated records
  • Low TTL – e.g., 60 sec.
    • More traffic on Route 53 ($$)
    • Records are outdated for less time
    • Easy to change records
  • Except for Alias records, TTL is mandatory for each DNS record

# CNAME vs Alias

  • AWS Resources (Load Balancer, CloudFront...) expose an AWS hostname:
    • lb1-1234.us-east-2.elb.amazonaws.com and you want myapp.mydomain.com
  • CNAME:
    • Points a hostname to any other hostname. (app.mydomain.com => blabla.anything.com)
    • ONLY FOR NON ROOT DOMAIN (aka. something.mydomain.com)
  • Alias:
    • Points a hostname to an AWS Resource (app.mydomain.com => blabla.amazonaws.com)
    • Works for ROOT DOMAIN and NON ROOT DOMAIN (aka mydomain.com)
    • Free of charge
    • Native health check

# Alias Records

  • Maps a hostname to an AWS resource
  • An extension to DNS functionality
  • Automatically recognizes changes in the resource’s IP addresses
  • Unlike CNAME, it can be used for the top node of a DNS namespace (Zone Apex), e.g.: example.com
  • Alias Record is always of type A/AAAA for AWS resources (IPv4 / IPv6)
  • You can’t set the TTL
Record Name Type Value
example.com A MyALB-123456789.useast1.elb.amazonaws.com

Alias Records Targets

  • Elastic Load Balancers
  • CloudFront Distributions
  • API Gateway
  • Elastic Beanstalk environments
  • S3 Websites
  • VPC Interface Endpoints
  • Global Accelerator accelerator
  • Route 53 record in the same hosted zone
  • You cannot set an ALIAS record for an EC2 DNS name

← Network abbreviations →