Route 53 DNS and Routing Policies

What it is

The Domain Name System (DNS) turns names such as www.example.com into IP addresses. Amazon Route 53 is the AWS DNS service. It can register domains, host the DNS records for a domain, check the health of endpoints, and route users to the best endpoint.

A hosted zone holds the records for one domain. A public hosted zone answers queries from the internet, and a private hosted zone answers only for the VPCs you associate with it.

How it works

Record types

An alias record can point to a CloudFront distribution, a load balancer, an API Gateway endpoint, an S3 website endpoint, a Global Accelerator and other AWS resources. Alias queries to AWS resources are not charged, and an alias can be used at the zone apex (example.com), where a CNAME is not allowed. Alias answers follow the target's address changes automatically.

{
  "Changes": [{
    "Action": "UPSERT",
    "ResourceRecordSet": {
      "Name": "www.example.com",
      "Type": "A",
      "AliasTarget": {
        "HostedZoneId": "Z0000000EXAMPLE",
        "DNSName": "my-alb-123456.us-east-1.elb.amazonaws.com",
        "EvaluateTargetHealth": true
      }
    }
  }]
}

This change batch is applied with aws route53 change-resource-record-sets --hosted-zone-id <zone> --change-batch file://change.json. The HostedZoneId inside the alias is the zone of the target service, not your own.

The TTL (time to live) tells resolvers how long they may cache an answer. Lower it before a planned change so updates spread faster.

Routing policies

Geolocation is about where the user is, and latency is about network speed. They can give different results, so read the wording of the question.

Health checks

Health checks probe an endpoint over HTTP, HTTPS or TCP, or watch a CloudWatch alarm, or combine other checks. Records linked to a health check are removed from answers when unhealthy.

Failover, weighted, latency, geolocation and multivalue records can use them. For an alias to an AWS resource, "evaluate target health" uses the resource's own health.

Private hosted zones

A private hosted zone resolves names only inside associated VPCs. The VPCs must have DNS support and DNS hostnames turned on. This is how you give internal names, such as db.internal.example.com, to private resources, and you can use the same name publicly and privately (split horizon DNS) with different answers.

Route 53 Resolver for hybrid DNS

Every VPC has a built in Amazon provided DNS resolver. For hybrid networks, Resolver endpoints extend it.

• Inbound endpoint: lets on premises servers send queries to Route 53 Resolver, to resolve AWS private names.
• Outbound endpoint: with forwarding rules, sends queries for chosen domains from the VPC to on premises DNS servers.

Domain registration

Route 53 can register and renew domains. If you register a domain elsewhere, point its name server records at the four name servers of your hosted zone.