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Difficulty: MediumAmazon Route 53 DNS Configuration and Routing Policies

A SysOps Administrator is configuring DNS resolution for a service endpoint at app.example.com. The service is hosted behind three Application Load Balancers (ALBs) located in different AWS Regions. The administrator wants to use DNS-based routing that returns the IP addresses of all healthy ALBs in response to DNS queries, while automatically removing any ALB that fails its health checks from DNS responses.

Which Route 53 configuration will meet these requirements?

  1. Create three Alias A records using the Multivalue Answer routing policy, targeting the DNS names of the respective ALBs, and enable Evaluate Target Health on each record.Answer
  2. B
    Create three CNAME records using the Multivalue Answer routing policy, targeting the DNS names of the respective ALBs, and enable Evaluate Target Health on each record.
  3. C
    Create three Alias A records using the Failover routing policy, designating one ALB as primary and the other two as secondary, and configure health checks for each.
  4. D
    Create a single CNAME record containing a comma-separated list of the three ALB DNS names, and associate a Route 53 health check with the CNAME record.

Answer

Create three Alias A records using the Multivalue Answer routing policy, targeting the DNS names of the respective ALBs, and enable Evaluate Target Health on each record.
The correct configuration uses Alias A records configured with the Multivalue Answer routing policy. Alias A records are natively integrated with Application Load Balancers (ALBs) and allow Route 53 to check their health using the 'Evaluate Target Health' setting. The Multivalue Answer routing policy returns multiple healthy records (up to eight) in response to a single DNS query, distributing traffic across all three healthy ALBs and removing any ALB that fails its health checks.

Step-by-Step Solution

1
Determine the appropriate record type to interface with Application Load Balancers.
Alias A records are selected instead of CNAME records.
Alias A records allow Route 53 to map the domain name directly to the load balancer's IP addresses and enable native health evaluation.
2
Select the routing policy that supports returning multiple healthy endpoints.
Multivalue Answer routing is selected.
Multivalue Answer routing allows Route 53 to return up to eight healthy IP addresses in response to a DNS query, providing DNS-based load balancing.
3
Configure health checking for the endpoints.
Set Evaluate Target Health to Yes on all three Alias A records.
This configuration allows Route 53 to query the target group health checks of the ALBs and automatically filter out unhealthy endpoints from the DNS responses.

Key Concept

Multivalue Answer routing combined with Alias A records and 'Evaluate Target Health' allows Route 53 to act as a basic load balancer by returning multiple IP addresses and automatically filtering out unhealthy resources.

Alternative Method

As an alternative, a Weighted routing policy could be configured with equal weights on each Alias A record. However, Weighted routing only returns a single record per DNS query, whereas Multivalue Answer routing returns multiple records, allowing client applications to retry alternative IP addresses if one becomes unreachable.
Estimated Time:1m 30s
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Amazon Route 53 DNS Configuration and Routing Policies

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