AWS Route 53

Record Types

• A: map a hostname to IPv4
• AAAA: map a hostname to IPv6
• CNAME: map a hostname to another hostname
  • the target is a domain name which must have an A or AAAA record
  • cannot create CNAME record for the top node of the a DNS namespace
    • example.com => no, www.example.com => yes
• NS: name server for the Hosted Zone
  • control how traffic is routed for a domain

Host Zone

• a container that holds information about how you want to route traffic for a domain
• public host zone: determines how traffic is routed on the internet
• private host zone: determines how traffic is routed within a VPC

TTL

• the client will cache the DNS query result for TTL seconds

CNAME vs Alias

• CNAME

  • maps a hostname to any other hostname (point to Load Balancer, CloudFront)
  • only for non-ROOT domain (not for mydomain.com)

• Alias

  • maps a hostname to an AWS resource
  • works for both ROOT domain (mydomain.com) and non-ROOT domain(abc.mydomain.com)
  • automatically recognize the changes in the resource's IP addresses
  • free of charge
  • native health check
  • targets
    • ELB, CloudFormation Distributions, API Gateway, S3 websites, VPC interface endpoints, Global Accelerator
    • Route 53 record in the same hosted zone
    • NOT for an EC2 DNS name

• difference

  • Alias can be used for the top node of a DNS namespace (Zone Apex)
  • Alias record is always of type A/AAAA for AWS resources

• for example: we have a ALB: my-backend.ap-southeast-2.elb.amazonaws.com, the following two configs are the same

  • CNAME: my-backend.my-domain.com => my-backend.ap-southeast-2.elb.amazonaws.com
  • A (Alias): my-backend.my-domain.com => my-backend.ap-southeast-2.elb.amazonaws.com

Routing Policies

• define how Route 53 responds to DNS queries

• DNS doesn't route any traffic, it only response to DNS queries

• Simple

  • typically route traffic to a single resource
  • can specify multiple values in the same record, a random one is chosen by the client
  • when alias is enabled, specify only one AWS resource
  • cannot be associated with health checks

• Weight

  • control the % of the requests that go to each specific resource
  • DNS records must have the same name and type
  • use cases:
    • load balancing between regions
    • testing new applications

• Latency

  • route traffic to resources in the AWS region that provides the lowest latency
  • all resources must be in AWS regions

• Failover

  • route traffic to a resource when the resource is healthy or to a different resource when the first resource is unhealthy
  • primary record
  • secondary record (failover)

• Geolocation

  • based on geographic location of your users
  • Location: continents, countries/regions

• Geoproximity

  • based on geographic location of your users
  • location type: Coordinates, AWS local zone group, AWS Region

• IP-based

  • based on user's IP address, define IP address range (CIDR)

• multi value

  • return multiple values (such as IP addresses) for the DNS query
  • can work with health checks, only healthy resources are returned

Routing traffic to a website that is hosted in a S3 bucket

• a registered domain
• a S3 bucket that's configured to host a static website, and the bucket name must be the same as your domain or subdomain
  • for example, if you use the subdomain, blog.daniel.com, the bucket name must be blog.daniel.com
• an S3 bucket configured as a website endpoint doesn't support SSL/TLS, so you need to route traffic to the CloudFront distribution and use the S3 bucket as the origin for the distribution

Active-active and active-passive failover

• Active-active failover

  • you configure active-active failover using any routing policy other than failover
  • you want all of your resources to be available the majority of the time; when a resource becomes unavailable, Route 53 can detect that it's unhealthy and stop including it when responding to queries
  • all the records that have the same name, the same type (such as A or AAAA) and the same routing policy (such as weighted or latency) are active unless Route 53 considers them unhealthy

• Active-passive failover

  • you configure active-passive failover using the failover routing policy
  • you want a primary resource or group of resources to be available the majority of the time and you want a secondary resource or group of resources to be on standby in case all the primary resources become unavailable
  • when responding to queries, Route 53 includes only the healthy primary resources; if all the primary resources are unhealthy, Route53 begins to include only the health secondary resources