As an AWS Administrator, you have set up an ELB within a couple of Availability Zones. The ELB distributes application traffic to an Auto Scaling group with session affinity enabled. You notice that the traffic is not being evenly distributed across the AZ’s. Which option may help to alleviate this issue? Choose an answer from the below options.

Answer options:

A.Disable sticky sessions on the ELB.B.Reduce the frequency of the health checks.
C.Increase the number of instances hosting the web application in each AZ.
D.Recreate the ELB again.

Answer – A
The traffic is not evenly distributed across the instances in multiple AZs. That means the traffic is going to only specific EC2 instances. This happens when either the instances that are not receiving the traffic are unhealthy or the instances receiving the traffic are holding onto the session.
This scenario does not mention any unhealthy instances. So, it is most likely related to instances holding onto sessions. This means the ELB has sticky sessions enabled.
Option A is CORRECT because this situation occurs when ELB has sticky sessions or session affinity enabled.
Option B is incorrect because reducing the frequency of health checks will not force the even distribution of the traffic.
Option C is incorrect because if sticky sessions are enabled, increasing the number of instances in each AZ will not help receive the traffic. In fact, more instances will remain idle now.
Option D is incorrect because recreating ELB again will not resolve this issue.
More information on ELB Sticky Sessions:
The load balancer uses a special cookie to track the instance for each request to each listener. When the load balancer receives a request, it first checks to see if this cookie is present in the request. If so, the request is sent to the instance specified in the cookie. If there is no cookie, the load balancer chooses an instance based on the existing load balancing algorithm. A cookie is inserted into the response for binding subsequent requests from the same user to that instance. The stickiness policy configuration defines a cookie expiration, which establishes the duration of validity for each cookie.
This could be a reason as to why the sessions are going to a certain AZ.
For more information on ELB sticky sessions, please refer to the below URL-
http://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-sticky-sessions.html