AWS SOA-C02 Drill: Route 53 Record Types - Choosing ALIAS for Load Balancer DNS

Jeff’s Note

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Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Site Reliability Engineer (SRE) responsible for maintaining high availability and automation.

For SOA-C02 candidates, the confusion often lies in which DNS record type Route 53 supports for root domain ALBs. In production, this is about knowing exactly when to use ALIAS records instead of CNAME to avoid DNS resolution errors and comply with DNS standards. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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TechX Solutions is launching a new customer-facing website hosted on Amazon EC2 instances behind an Application Load Balancer (ALB). They use Amazon Route 53 for DNS management and want users to access the site via the root domain techxsolutions.com (not a subdomain).

The Requirement:

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Which type of DNS record should TechX Solutions create in Route 53 to point the root domain (techxsolutions.com) to the Application Load Balancer?

The Options

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• A) CNAME
• B) SOA
• C) TXT
• D) ALIAS

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leave a comment:

Correct Answer

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D) ALIAS

Quick Insight: The SysOps Imperative

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• Route 53 ALIAS records are a proprietary extension that lets you map apex/root domains directly to AWS resources like ALBs without violating DNS RFCs.
• Using a CNAME at the root domain is disallowed because DNS standards do not permit CNAME records at the zone apex.
• ALIAS records also provide automatic health checks and failover integration.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Option D: ALIAS

The Winning Logic

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This is the correct choice because:

• DNS standards prohibit placing CNAME records on the zone apex (root domain), which would cause resolution failures or clashes with other records like SOA and NS.
• Route 53 provides ALIAS records that behave like CNAMEs under the hood but resolve to an AWS resource’s IP addresses, supporting apex domain use cases.
• ALIAS records are free to Route 53 users and integrate seamlessly with AWS Load Balancers, CloudFront distributions, and S3 website endpoints.
• This allows TechX Solutions’ domain techxsolutions.com to resolve directly to their ALB without breaking DNS protocol rules.

The Trap (Distractor Analysis)

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• Why not A) CNAME?
  Although commonly used for subdomains, CNAME records cannot be placed on the root domain. This would violate DNS RFC 1034 and break other critical DNS records.

• Why not B) SOA?
  SOA records define authoritative zone information—they are not used for direct URL routing or pointing domains to load balancers.

• Why not C) TXT?
  TXT records store textual data, often for verification or policy purposes, not for DNS pointing or aliasing.

The Technical Blueprint

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# Example CLI to create an ALIAS record in Route53 pointing apex domain to an ALB

aws route53 change-resource-record-sets --hosted-zone-id Z3M3LMPEXAMPLE \
--change-batch '{
  "Changes": [{
    "Action": "UPSERT",
    "ResourceRecordSet": {
      "Name": "techxsolutions.com",
      "Type": "A",
      "AliasTarget": {
        "HostedZoneId": "Z35SXDOTRQ7X7K", # ALB hosted zone ID
        "DNSName": "dualstack.techx-alb-123456.us-east-1.elb.amazonaws.com",
        "EvaluateTargetHealth": true
      }
    }
  }]
}'

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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For the exam, always pick ALIAS when you need to point a root (apex) domain to AWS resources like ALBs, CloudFront, or S3 websites.

Real World

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In reality, if you are using other DNS providers, you might use ANAME or ALIAS-like features or handle apex to www redirects to circumvent CNAME apex limitations.

(CTA) Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the SOA-C02 exam.