DVA-C02 Troubleshooting and Optimization Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  The target group is using an HTTPS health check but the instances only support HTTP.

  Why it's wrong here

  If the target group's health check protocol (HTTPS) does not match the instance's supported protocol (HTTP), the load balancer will mark the instances as unhealthy. Consequently, it will not forward traffic to them, or if it does, the backend will fail to respond correctly, resulting in an HTTP 502 Bad Gateway error. A 504 specifically means the load balancer waited for a response but didn't get one within its timeout, not a protocol mismatch.

• ✗

  The load balancer's cross-zone load balancing is disabled.

  Why it's wrong here

  Disabling cross-zone load balancing means that each load balancer node only distributes traffic to targets within its own Availability Zone. While this can lead to uneven traffic distribution and potential overload in specific zones, it does not directly cause an HTTP 504 Gateway Timeout. A 504 error indicates a timeout waiting for a response from a *single* backend instance, not a broad distribution problem across zones.

• ✓

  The load balancer idle timeout is set too low, and the application takes longer than the timeout to respond.

  Why this is correct

  The load balancer idle timeout specifies the maximum duration the load balancer will wait for a response from a registered target before closing the connection. If the backend application takes longer to process a request and send a response than this configured timeout, the load balancer will terminate the connection. This action directly results in an HTTP 504 Gateway Timeout error being returned to the client, indicating a lack of timely response.

• ✗

  The security group for the EC2 instances is missing an inbound rule for the load balancer.

  Why it's wrong here

  A missing inbound rule in the EC2 instance security group for the load balancer prevents the load balancer from establishing a TCP connection to the backend instance. This connection failure typically manifests as a connection timeout from the load balancer's perspective, often leading to HTTP 502 Bad Gateway or 503 Service Unavailable errors. A 504 Gateway Timeout, however, implies a connection was successfully established but no response was received within the specified idle period.