What is DNS?

• Domain Name System which translates the human friendly hostnames into the machine IP addresses

• www.google.com => 172.217.18.36

• DNS is the backbone of the internet

• DNS uses hierarchical naming structure: .com, .example.com, www.example.com, api.example.com

DNS Terminologies

• Domain Registrar: Amazon Route 53, GoDaddy, Hostinger, ...

• DNS Records: A, AAAA, CNAME, NS, ...

• Zone File: contains DNS records

• Name Server: resolves DNS queries (Authoritative or Non-Authoritative)

• Top Level Domain (TLD): .com, .us, .in, .gov, ...

• Second Level Domain (SLD): amazon.com, google.com, ...

• Sub Domain: www.example.com, ...

• Full Qualified Domain Name (FQDN): api.www.example.com

Amazon Route 53 Overview

• A highly available, scalable, fully managed and Authoritative DNS

  • Authoritative = the customer (you) can update the DNS records

• Route 53 is also a Domain Registrar

• Ability to check the health of your resources

• Why 53? 53 is a reference to the traditional DNS port

Route 53 - Records

• Records describes 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 responses to queries
  • TTL - amount of time the record cached at DNS Resolvers

• Route 53 supports the following DNS record type

  • (must know) A / AAAA / CNAME / NS
  • (advanced) CAA / DS / MX / NAPTR / PRT / SOA / TXT / SPF / SRV

Record Types

• A - maps a hostname to IPv4

• AAAA - maps a hostname to IPv6

• CNAME - maps a hostname to another hostname

  • The target is a domain name which must have an A or AAAA record
  • Can't create a CNAME record for the top node of a DNS namespace (Zone Apex)
  • Example: you can't create for the example.com, but you can create for www.example.com

• NS - Name Servers for the Hosted Zone

  • Control how traffic is routed for a domain

Hosted Zones

• A container for records that define how to route traffic to a domain and its subdomains

• Public Hosted Zones - contains records that specify how you route traffic on the Internet (public domain names)

• Private Hosted Zones - contains records that specify how you route traffic within one or more VPCs (private domain names)

CNAME vs Alias

• AWS Resources (Load Balancer, CloudFront,...) expose an AWS hostname.
  ex. lb1-1234.us-east-2.alb.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

• Alias:

  • Points a hostname to an AWS Resoure (app.mydomain.com => blabla.amazonaws.com)
  • Works for ROOT DOMAIN and NON ROOT DOMAIN
  • Free of charge
  • Native health check
  • Alias Record is always of type A/AAAA for AWS resources (IPv4/IPv6)
  • You can't set TTL

Alias Records Targets

• Elastic Load Balancers

• CloudFront Distribution

• 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