Route 53 Routing Policies and Failover#
DNS is the cheapest high-availability tool AWS gives you. The exam wants you to match a business requirement to one of seven routing policies - the words “latency”, “geolocation”, “failover” and “weighted” each map to exactly one answer.
The routing policies#
| Policy | What it does | Scenario keyword |
|---|---|---|
| Simple | One record, random answer | “single resource”, no smartness needed |
| Weighted | Split traffic by % | “canary 10% to the new version”, “A/B test” |
| Latency | Send users to the lowest latency region | “best performance for the user” |
| Failover | Active-passive; health check flips DNS | “disaster recovery”, “passive standby” |
| Geolocation | Route by user’s location | “content licensing”, “different content per country” |
| Geoproximity | Route by resource location + bias | “shift more traffic to region X” |
| IP-based | Route by user’s IP CIDR | “these offices go to that endpoint” |
| Multivalue answer | Up to 8 healthy records, client picks | “poor man’s load balancing” |
Health checks and failover#
- Route 53 health checks monitor endpoints (HTTP/TCP, string match), or CloudWatch alarms as the source
- Failover routing + health check = automatic active-passive DR (disaster recovery): primary unhealthy → DNS points at secondary
- Note the DNS TTL (time to live) effect: failover is only as fast as the record’s TTL (see dns-ttl-and-caching)
Classic pattern - static site failover to S3 (Simple Storage Service):
flowchart LR
hc[Health check: primary] -->|healthy| a[Primary: EC2/ALB]
hc -->|unhealthy| b[Secondary: S3 static website]Alias vs CNAME - a favorite trick#
| Alias record | CNAME | |
|---|---|---|
| Apex (zone root) | Works | Not allowed |
| Points to | AWS resources (ALB (Application Load Balancer), CloudFront, S3 website, API GW…) | Any DNS name |
| Charges | Free for AWS targets | Normal DNS queries |
“Point the root domain (example.com, no www) at an ALB” → Alias record, always.
Hosted zones (public vs private) and record types are covered in my hands-on notes: route-53-hosted-zones, cloudfront-with-dns.
Route 53 / CloudFront vs AWS Global Accelerator#
This comparison comes up whenever global latency or regional failover is mentioned:
| CloudFront | AWS Global Accelerator | |
|---|---|---|
| What it does | Caches content (HTTP/HTTPS) at 600+ edge locations | Proxies TCP/UDP packets onto the AWS backbone via 2 static Anycast IPs (no caching!) |
| Protocols | HTTP / HTTPS / WebSocket | Any TCP or UDP (gaming, IoT, VoIP, custom ports, HTTP) |
| Static IPs for whitelisting | No (dynamic edge IPs) | Yes — 2 static Anycast IPv4 addresses |
| Failover speed | Depends on origin health / DNS | < 30 seconds (no client DNS TTL caching issues because the Anycast IP never changes!) |
| Targets | S3, ALB, API Gateway, custom HTTP | ALB, NLB, EC2 instances, Elastic IPs across multiple regions |
Not: Kısa hatırlatma — “latency” en hızlı bölgeye, “geolocation” kullanıcı neredeyse oraya, “weighted” yüzdelik dağılıma, “failover” sağlık kontrolüne bakar. Soruda “2 statik IP (whitelisting), UDP/TCP oyun/finans trafiği veya DNS TTL beklemeden anında bölgesel failover” geçiyorsa cevap AWS Global Accelerator‘dır.
Exam check#
Q1: A company wants 10% of traffic to go to a new application version and 90% to the current one, gradually increasing. Which routing policy?
- A) Latency
- B) Weighted
- C) Geolocation
- D) Simple
Cevabı göster
Answer: B. Percentage-based split = weighted.
Q2: Users in Europe must receive European-specific content, and users in the US must receive US content. Which policy?
- A) Latency routing
- B) Geolocation routing
- C) Failover routing
- D) Multivalue answer
Cevabı göster
Answer: B. Content varies by where the user is = geolocation. Latency would pick the fastest, not the “correct” content.
Q3: A primary web app in us-east-1 must automatically fail over to an S3 static website in eu-west-1 when its health check fails. Which routing policy?
- A) Weighted
- B) Failover
- C) Geoproximity
- D) IP-based
Cevabı göster
Answer: B. Active-passive + health check = failover routing.
Ozet#
- Simple = tek kaynak, Weighted = yuzde dagilim, Latency = en hizli bolge
- Failover = saglik kontrolu + aktif-pasif DR
- Geolocation = icerik ulkeye gore degisir, Geoproximity = bolgeye yakinlik + bias
- IP-based = CIDR eslesme, Multivalue = 8’e kadar saglikli kayit
- Alias = apex’te calisir, AWS hedeflerine ucretsiz; CNAME apex’te yasak
- DNS TTL = failover hizini sinirlar