How to Shift Blue/Green ALB Traffic Gradually with Route 53 DNS?
A company uses two production environments for deployments. A blue stack and a green stack are each behind a unique Application Load Balancer (ALB). The company wants to use DNS to send some traffic to green and gradually increase traffic over time. The company wants automatic tailback if green becomes unhealthy. Which DNS configuration will meet these requirements?
Community Insight
The question tests whether you can pick the DNS routing policy that offers both proportional traffic control and health-based removal — weighted alias records with health checks — rather than a policy that only changes latency or failover behaviour.
Using Route 53 weighted alias records that each point at a blue or green ALB lets you dial a percentage of DNS traffic toward green and raise it over time. Attaching Route 53 health checks to those records gives the automatic fallback the company requires when green turns unhealthy.
Choosing latency-based records (B) because they 'steer a small percentage', when latency records distribute by measured network latency and give no weight dial for a deliberate 5% → 50% → 100% ramp.
Community Discussion (1 comments)
Comments & Corrections
No comments yet — spotted an error or have a note? Share it below.
Expert Analysis
Why the Answer Is Correct
Weighted alias records are the only Route 53 policy in these options that lets you assign an explicit numeric weight per record, so a 90/10 split for blue/green becomes a 50/50 and then a 0/100 as the deployment progresses. Because each record points at an ALB alias, Route 53 resolves to the load balancer's DNS name without extra lookups or chargeable queries against the alias target. Attaching a Route 53 health check to each record means an unhealthy green ALB is dropped from DNS answers and its weight is effectively redistributed to blue, which is exactly the automatic fallback requested. Adjusting weights is a simple record update, so no listener or target-group surgery is required during the deployment.Why the Other Options Are Wrong
Latency-based routing (B) selects the record with the lowest measured latency between the resolver and the AWS Region; it cannot be told to send 'some traffic' to green, so a small deliberate percentage ramp is not achievable and the checker-latency dashboard adds nothing. Option C is not a DNS configuration at all — target groups belong to a single ALB's listener rules, and with two separate ALBs there is no shared listener to weight against, so DNS never participates in the split. Option D misuses failover records: failover routing is primary/secondary with health-based cutover, there is no 50/50 weighting, and a healthy primary would simply take all traffic.Community Comment Notes
Bad_Mat's comment is brief and to the point, stating that the answer is A with "Create Amazon Route 53 weighted alias records that point to each ALB" and health checks attached, weights adjusted during the deployment. That matches the standard blue/green pattern documented for Route 53 and reinforces that the health check, not the weight, is what produces the automatic rollback. No commenter argued for the latency or failover variants, so there is no substantive dissent to reconcile here.Official Reference
Exam Strategy
When a scenario says 'send some traffic' plus 'gradually increase' plus 'automatic fallback', map those three phrases directly onto weighted records, adjustable weights and health checks. Latency and failover policies sound plausible but cannot express a percentage, so eliminate them first.
Frequently Asked Questions
Why can't latency-based routing send a small percentage of traffic to green?
Latency records are chosen by measured resolver-to-Region latency, not by an operator-set percentage, so you cannot dial a deliberate 5% ramp toward the green ALB.
How does Route 53 fall back automatically if the green ALB becomes unhealthy?
Each weighted alias record carries a health check; an unhealthy green record is excluded from answers, so all DNS responses go to the healthy blue ALB without manual intervention.
Related Analysis
Practice All SOA-C03 Questions
Access 100 questions with complete answers and detailed explanations.
View Full SOA-C03 Practice Test →