AWS SOA-C02 Drill: Route 53 DNS Routing Policies - Precision Traffic Splitting

The Jeff’s Note (Contextual Hook)

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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).

For SOA-C02 candidates, the confusion often lies in choosing the right Route 53 routing policy for controlled traffic distribution. In production, this is about knowing exactly which routing policy supports weighted traffic splits rather than failover or latency balancing. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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AcmeCloud Solutions is launching an upgraded version of its core web application. The SRE team needs to roll out the new version gradually to only 20% of its users while 80% continue accessing the current version. They use Amazon Route 53 to manage DNS for the application’s domain and want to implement this controlled deployment via DNS routing policies.

The Requirement:

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Design a Route 53 DNS configuration that routes 20% of user traffic to the new application servers and 80% to the existing servers, ensuring a stable and measurable partial rollout.

The Options

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• A) Create a failover routing policy. Configure 80% of traffic to the original servers as the primary record and 20% to the new servers as the failover record.
• B) Create a multivalue answer routing policy with 4 records pointing to the original servers and 1 record pointing to the new servers.
• C) Create a latency-based routing policy. Configure one record pointing to the original servers with a weight of 80 and one record pointing to the new servers with a weight of 20.
• D) Create a weighted routing policy. Assign a weight of 80 to the original servers’ record and 20 to the new servers’ record.

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Correct Answer

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D

Quick Insight: The SOA-C02 Operational Excellence Imperative

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• Weighted routing policy is the only Route 53 strategy that explicitly supports traffic percentage splits.
• Failover routing is intended for availability failovers, not traffic distribution.
• Multivalue answer routing does not guarantee exact traffic splits—just multiple records to increase availability.
• Latency routing directs based on latency measurements, not fixed traffic percentages.

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

The Winning Logic

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Weighted routing in Amazon Route 53 lets you specify weights for multiple resource record sets, directly controlling the proportion of DNS queries sent to each endpoint. By assigning an 80 weight to the existing servers and 20 to the new ones, the DNS resolver approximates sending 20% of the users to the new version — perfect for canary or phased rollouts.

• Weighted routing works at the DNS resolution level, giving precise traffic distribution control.
• This approach enables parallel infrastructure during rollout and easy rollback by adjusting or removing weights.

The Trap (Distractor Analysis):

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• Why not A?
  Failover routing is designed for high availability, routing traffic to the primary resource until a health check fails, then shifting all traffic to a failover. It does not support traffic splitting percentages.
• Why not B?
  Multivalue answer routing returns multiple healthy IP addresses randomly, without guaranteed traffic percentages. It’s used primarily for basic load balancing and redundancy, not precise rollouts.
• Why not C?
  Latency-based routing directs traffic based on lowest latency to endpoints, not fixed traffic proportions, so it can’t guarantee a 20-80 split.

The Technical Blueprint

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# CLI snippet to set weighted records in Route 53
aws route53 change-resource-record-sets --hosted-zone-id Z123EXAMPLE \
--change-batch '{
  "Changes":[
    {
      "Action":"UPSERT",
      "ResourceRecordSet":{
        "Name":"app.example.com",
        "Type":"A",
        "Weight":80,
        "SetIdentifier":"CurrentAppVersion",
        "ResourceRecords":[{"Value":"192.0.2.1"}],
        "TTL":60
      }
    },
    {
      "Action":"UPSERT",
      "ResourceRecordSet":{
        "Name":"app.example.com",
        "Type":"A",
        "Weight":20,
        "SetIdentifier":"NewAppVersion",
        "ResourceRecords":[{"Value":"192.0.2.2"}],
        "TTL":60
      }
    }
  ]
}'

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 Weighted Routing when you see percent-based traffic splitting requirements.

Real World

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In practice, we might complement weighted routing with health checks and automation scripts to dynamically adjust weights based on rollout metrics and system health.

(CTA) Stop Guessing, Start Mastering

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Disclaimer

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