<strong>A development team is using Java/Tomcat to build up a new feature for an IOT project. They decided to create a new autoscaling group using a launch configuration that contained the latest AMI. And then they attached the new autoscaling group to the existing Classic ELB with a HTTP health check. After ELB passed the health check, they removed the old autoscaling group. Using this way, they were trying to implement the Blue/Green deployment. However, they found that the new autoscaling did not service properly and there were lots of Tomcat errors. Which below action should be done to reduce Tomcat errors?</strong>

Answer options:

A.The health check is not accurate. The Classic ELB health check should point to a endpoint or a webpage in the application to indicate when the instances are ready to receive traffic.
B.The health check is not configured properly. The classic ELB should be replaced using an application load balancer and the HTTPS health check is required.
C.The classic ELB or network ELB cannot meet the need. The application load balancer should be used as it is able to check the application status. In this case, the application is not ready yet when the ELB health check passed.
D.After the new autoscaling group is created, wait for a longer time firstly so that the instances are ready to service the traffic. Then attach the autoscaling group to the ELB.

Answer -
Option A
We should use ELB health check to know when we should start sending traffic to a new set of instances. For Java apps running on Tomcat, even when the EC2 instance has finished its boot sequence, there is so much that can happen at the application level before the app is ready for traffic - initializing data structures, reading configuration, configuring logging, warming a cache. The user should create an endpoint/page in the application and let it tell you when it is ready to receive traffic. The classic HTTP health check is able to ping this new page and understand when the new instances are truly ready to service traffic.
Option B is incorrect: because classic HTTP ELB health check is able to meet the need.
HTTPS is also not necessary.
Option C is incorrect: because classic HTTP ELB health check is able to meet the need.
Option D is incorrect because ELB health check should be used to avoid any manual check on the instance status.