DOP-C02 Question 323
Single answerAn organization is running a highly available web application in AWS using an Auto Scaling group for EC2 instances behind an Application Load Balancer (ALB). Recently, users reported intermittent 5xx errors when accessing the application. Upon inspecting ALB logs, you notice frequent HTTP 504 errors. What is the MOST appropriate step to troubleshoot and resolve this issue?
- A
Increase the idle timeout setting for the Application Load Balancer.
- B
Enable ALB access logs and inspect the request details for anomalous patterns.
- C
Verify the health check configuration of the Auto Scaling group and increase the health check interval.
- D
Review the application logs on the EC2 instances to identify potential performance bottlenecks.
Show answer and explanation
Correct answer: A
Explanation
HTTP 504 errors in ALB indicate that the load balancer did not receive a response from the backend within the configured idle timeout period. Increasing the ALB idle timeout setting is the most appropriate immediate action to resolve this issue. While additional steps like reviewing application logs or enabling access logs might help diagnose deeper root causes, they do not directly address the immediate problem of timeout settings.
- A. Correct.
Correct. HTTP 504 errors indicate a gateway timeout, which typically occurs when the backend does not respond within the ALB's configured timeout. Increasing the idle timeout setting allows more time for the backend to respond.
- B. Incorrect.
Incorrect. While enabling ALB access logs might provide additional information, it does not directly address the issue of HTTP 504 errors caused by backend timeout.
- C. Incorrect.
Incorrect. Adjusting the health check configuration will affect how the Auto Scaling group determines instance health but does not resolve the gateway timeout issue linked to the ALB.
- D. Incorrect.
Incorrect. Reviewing application logs may help identify performance bottlenecks, but it does not directly address the immediate issue of HTTP 504 errors caused by ALB timeout settings.