AWS Certified Solutions Architect - Associate
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A company has a web application hosted over 10 Amazon EC2 instances with traffic directed by Amazon Route 53. The company occasionally experiences a timeout error when attempting to browse the application. The networking team finds that some DNS queries return IP addresses of unhealthy instances, resulting in the timeout error.
What should a solutions architect implement to overcome these timeout errors?
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UAnonymous
A
Create a Route 53 simple routing policy record for each EC2 instance. Associate a health check with each record.
B
Create a Route 53 failover routing policy record for each EC2 instance. Associate a health check with each record.
C
Create an Amazon CloudFront distribution with EC2 instances as its origin. Associate a health check with the EC2 instances.
D
Create an Application Load Balancer (ALB) with a health check in front of the EC2 instances. Route to the ALB from Route 53.
Explanation:
Explanation
The correct answer is D because:
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Problem Analysis: The issue is that Route 53 DNS queries are returning IP addresses of unhealthy EC2 instances, causing timeout errors. Route 53 health checks can help, but they have limitations:
- Route 53 health checks operate at the DNS level and have TTL (Time to Live) considerations
- When a client caches DNS responses, they may continue using unhealthy IP addresses until the cache expires
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Solution Architecture:
- Application Load Balancer (ALB) with health checks provides continuous monitoring of backend instances
- ALB automatically routes traffic only to healthy instances in real-time
- Route 53 points to the ALB DNS name, which resolves to healthy instances
- This creates a two-tier architecture: DNS routing (Route 53) → Load balancing (ALB) → EC2 instances
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Why other options are incorrect:
- A (Simple routing with health checks): Route 53 simple routing with health checks still has DNS caching issues. Clients may cache unhealthy IP addresses.
- B (Failover routing): Failover routing is for active-passive scenarios, not for distributing traffic across multiple healthy instances.
- C (CloudFront): While CloudFront can help with caching and performance, it doesn't solve the fundamental issue of routing to unhealthy backend instances. CloudFront origins still need health monitoring.
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Best Practice: The recommended AWS pattern is to use an Application Load Balancer behind Route 53 for web applications. The ALB provides:
- Automatic health checks and instance registration/deregistration
- Real-time traffic routing to healthy instances
- Better handling of connection draining and instance replacement
- No DNS caching issues for end users
This solution ensures that users are always directed to healthy instances, eliminating the timeout errors caused by DNS returning unhealthy instance IPs.
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