You have created an Elastic Load Balancer with Duration-Based sticky sessions enabled in front of your six EC2 web application instances in US-West-2. For High Availability, there are three web application instances in Availability Zone 1 and three web application instances in Availability Zone 2. To load test, you set up a software-based load tester in Availability Zone 2 to send traffic to the Elastic Load Balancer, as well as letting several hundred users browse to the ELB’s hostname.

Answer options:

A.Create a software-based load tester in US-East-1 and test from there.
B.Force the software-based load tester to re-resolve DNS before every request.
C.Use a third party load-testing service to send requests from globally distributed clients.
D.Switch to application-controlled sticky sessions.

Answer – B and C
When you create an elastic load balancer, a default level of capacity is allocated and configured. As Elastic Load Balancing sees changes in the traffic profile, it will scale up or down. The time required for Elastic Load Balancing to scale can range from 1 to 7 minutes, depending on the changes in the traffic profile. When Elastic Load Balancing scales, it updates the DNS record with the new list of IP addresses. To ensure that clients are taking advantage of the increased capacity, Elastic Load Balancing uses a TTL setting on the DNS record of 60 seconds. It is critical that you factor this changing DNS record into your tests. If you do not ensure that DNS is re-resolved or use multiple test clients to simulate increased load, the test may continue to hit a single IP address when Elastic Load Balancing has actually allocated many more IP addresses. Because your end-users will not all be resolving to that single IP address, your test will not be a realistic sampling of real-world behavior.
Option A is incorrect because creating a load tester in US-East-1 is inconsequential since it is in a different region.
Option B is CORRECT because if you do not ensure that DNS is re-resolved, the test may continue to hit the single IP address.
Option C is CORRECT because if the requests come from globally distributed users, the DNS will not be resolved to a single IP address. The traffic would be distributed evenly across multiple instances.
Option D is incorrect because the traffic will be routed to the same back-end instances as the users continue to access your application. The load will not be evenly distributed across the AZs.
Please refer to the below article for more information.
http://aws.amazon.com/articles/1636185810492479