Route 53

Route 53 Quick Notes

Hosted Zones

• Public: Internet DNS for your domain.
• Private: Answers only inside associated VPCs (needs DNS hostnames + DNS resolution on the VPC).

A vs CNAME vs Alias

Record, Maps, Apex (naked domain)?

A, Name → IPv4, Yes

CNAME, Name → another name, No

Alias, Name → AWS resource, Yes

• Prefer Alias for ALB, CloudFront, API Gateway, Elastic Beanstalk, Global Accelerator, S3 website endpoints.
• Map www.example.com → app.provider.com (third party) → CNAME (Alias is for AWS resources).

Health Checks

• Separate objects that records can use; checkers are global.
• Types: endpoint, CloudWatch alarm, calculated (checks of checks).
• Unhealthy records are usually omitted from answers.

Routing Policies

Policy: When to use

Simple: Single resource; no health checks in this model

Failover: Active/passive DR

Multi-value: Up to 8 healthy records; not a load balancer replacement

Weighted: Traffic split / blue-green by weight

Latency-based: Lowest estimated latency Region

Geolocation: User’s geography bucket (country/continent) — licensing / geo rights

Geoproximity: Distance + optional bias to expand/shrink a Region’s area

Exam Contrasts

• Geo rights / block countries at DNS: Geolocation (pair with CloudFront georestriction / WAF as needed).
• Latency / Weighted / Failover: Do not enforce geo distribution rights.
• Mobile clients cache DNS: Weighted Route 53 shifts slowly — prefer Global Accelerator to dial traffic % without waiting on TTLs.
• Europe slow, stack in us-east-1: Extra web tier + latency routing (+ Aurora cross-Region read replicas).