AWS Route53

# DNS Terminologies

FQDN -> http://api.example.com

A highly available, scalable, fully managed and Authoritative DNS, and a Domain Registrar. 100% availability SLA

Route53 supports following DNS record types: A, AAAA, CNAME, NS; CAA, DS, MX, NAPTR, PTR, SOA, TXT, SPF, SRV

record types

A - hostname IPv4
AAAA - hostname IPv6
CNAME - another hostname
- the target is a domain name which must have an A or AAAA record
- eg. www.example.com -> example.com
NS - Name Servers for the hosted zone

Route53 supports Public/Private hosted zones. (mypublicdomain.com / company.internal)

CNAME vs Alias

CNAME
- Points a hostname to any other hostname
- ONLY FOR NON-ROOT DOMAIN (aka.something.mydomain.com)
Alias
- Points a hostname to an AWS Resource
- Works for ROOT DOMAIN and NON-ROOT DOMAIN (mydomain.com)
- Free of charge
- Native health check
- automatically recognizes changes in the resource’s IP address
- but can’t set the TTL
- targets
  - ELB
  - CloudFront
  - API Gateway
  - Beanstalk environment
  - S3
  - VPC interface endpoints
  - Global Accelerator
  - Route53 record

Simple
- route traffic to single/multiple value
- can specify multiple values in the same record
- if multiple values are returned, a random one is chosen by the client
- no health check
Weighted
- Control the % of the requests that go to each specific resource
- DNS records must have the same name and type
- health checks
- assign weight to 0 to prevent traffic
- if all records’ weight are 0, they will be treated equally
Failover
- active-passive
- active-active
Latency based
- Redirect to the resource which has the least latency
- latency is based on traffic between users and AWS Regions
- health check
Geolocation
- based on user location
- should create a “default” record
Multi-Value answer
Geoproximity
- ability to shift more traffic to resources based on the defined bias
- must use Route53 Traffic Flow to use this feature
IP-based (CIDRs)
Multi-Value
- up to 8 healthy records are returned for each query
- Multi-value is not a substitute for having an ELB

Health checks are only for public resources
About 15 global health checkers will check the endpoint health
- healthy/unhealthy threshold - 3 by default
- interval 30s
- if > 18% of health checkers report ok, Route53 considers it healthy
only pass when 2xx, 3xx status codes
Health Checks can be setup to pass / fail based on the text in the first 5120bytes of the response
calculated health checks (combination)
- OR, AND, NOT
- up to 256 child health checks
route53 health checkers are outside the VPC
- create a cloud-watch metric and associate a cloud-watch alarm, then create a health check that checks the alarm itself