SAA-C03 Question 534
Select 2A company is hosting a web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application is experiencing occasional spikes in traffic, and users have reported intermittent 504 Gateway Timeout errors during these spikes. What could be the MOST likely causes of this issue, and how can it be resolved?
- A
The health checks for the ALB are misconfigured, causing unhealthy targets to remain in service.
- B
The EC2 instances are under-provisioned and cannot handle the traffic spikes, leading to timeouts.
- C
The ALB is throttling traffic because it has reached its maximum capacity limit.
- D
The idle timeout for the ALB is too low, causing long-running requests to fail.
- E
The security group of the ALB is blocking traffic from reaching the EC2 instances.
Show answer and explanation
Correct answers: B, D
Explanation
504 Gateway Timeout errors usually indicate that the backend servers (EC2 instances) are not responding to the ALB within the expected time frame. Common causes include under-provisioned EC2 instances that cannot handle traffic spikes or an idle timeout that is too low for long-running requests. Ensuring the backend is properly scaled and adjusting the idle timeout setting on the ALB can help resolve such issues.
- A. Incorrect.
Health check misconfiguration would result in unhealthy targets being removed from service, not remaining active. This is unlikely to cause intermittent 504 errors.
- B. Correct.
Under-provisioned EC2 instances can lead to high latency or timeouts during traffic spikes, which can result in 504 Gateway Timeout errors.
- C. Incorrect.
ALBs are highly scalable and typically do not throttle traffic unless there are specific configurations or limits imposed. This is not a common cause of 504 errors.
- D. Correct.
A low idle timeout on the ALB can cause long-running requests to terminate before they are completed, leading to 504 errors.
- E. Incorrect.
If the security group was blocking traffic, the application would not work consistently. This would likely result in permanent connectivity issues rather than intermittent timeouts.