What should a solutions architect do to meet these requirements?

A company’s HTTP application is behind a Network Load Balancer (NLB). The NLB’s target group is configured to use an Amazon EC2 Auto Scaling group with multiple EC2 instances that run the web service.

The company notices that the NLB is not detecting HTTP errors for the application. These errors require a manual restart of the EC2 instances that run the web service. The company needs to improve the application’s availability without writing custom scripts or code.

What should a solutions architect do to meet these requirements?
A . Enable HTTP health checks on the NLB. supplying the URL of the company’s application.
B. Add a cron job to the EC2 instances to check the local application’s logs once each minute. If HTTP errors are detected, the application will restart.
C. Replace the NLB with an Application Load Balancer. Enable HTTP health checks by supplying the URL of the company’s application. Configure an Auto Scaling action to replace unhealthy instances.
D. Create an Amazon Cloud Watch alarm that monitors the UnhealthyHostCount metric for the NLB. Configure an Auto Scaling action to replace unhealthy instances when the alarm is in the ALARM state.

View Answer

Answer: C

Explanation:

Application availability: NLB cannot assure the availability of the application. This is because it bases its decisions solely on network and TCP-layer variables and has no awareness of the application at all. Generally, NLB determines availability based on the ability of a server to respond to ICMP ping or to correctly complete the three-way TCP handshake. ALB goes much deeper and is capable of determining availability based on not only a successful HTTP GET of a particular page but also the verification that the content is as was expected based on the input parameters.