A startup s photo-sharing site is deployed in a VPC. An ELB distributes web traffic across two subnets. ELB
session stickiness is configured to use the AWS-generated session cookie, with a session TTL of 5 minutes.
The webserver Auto Scaling Group is configured as: min-size=4, max-size=4.
The startups preparing for a public launch, by running load-testing software installed on a single EC2 instance
running in us-west-2
After 60 minutes of load-testing, the webserver logs show:
Which recommendations can help ensure load-testing HTTP requests are evenly distributed across the four
webservers? (Choose two.)
A.
Launch and run the load-tester EC2 instance from us-east-1 instead.
B.
Re-configure the load-testing software to re-resolve DNS for each web request.
C.
Use a 3rd-party load-testing service which offers globally-distributed test clients.
D.
Configure ELB and Auto Scaling to distribute across us-west-2a and us-west-2c.
E.
Configure ELB session stickiness to use the app-specific session cookie.
B. Re-configure the load-testing software to re-resolve DNS for each web request.
C. Use a 3rd-party load-testing service which offers globally-distributed test clients.
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I agree
B, C
http://www.aiotestking.com/amazon/which-recommendations-can-help-ensure-load-testing-http-requests-are-evenly-distributed-across-the-four-webservers/
I don’t think A b/c you will probably get the same results from A as you would from any other single place. All requests going to a single AZ
I don’t think D b/c demo users are being distributed
I don’t think E b/c the session cookie isn’t the problem, the problem is traffic from a single location keeps going to the same location
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Can anyone explain the answers? Also I am not clear how the HTTP requests got distributed only across Web Servers in us-west-2a. Please clarify.
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Click the link I provided; read the text on the page.
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C & E
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DNS Resolution (Why is needed to Control Load Testing Parameters)
If clients do not re-resolve the DNS at least once per minute, then the new resources Elastic Load Balancing adds to DNS will not be used by clients. This can mean that clients continue to overwhelm a small portion of the allocated Elastic Load Balancing resources, while overall Elastic Load Balancing is not being heavily utilized. This is not a problem that can occur in real-world scenarios, but it is a likely problem for load testing tools that do not offer the control needed to ensure that clients are re-resolving DNS frequently.
Sticky Sessions and Unique Clients (Why ELB session stickiness is an issue)
If sticky sessions are enabled, it is critical that the load test framework not re-use connections and clients in the tests, but rather it creates unique clients for each request. If this is not done, then the clients will constantly send traffic to the same Elastic Load Balancing resources and the same back-end instances, overwhelming what is potentially a very small amount of the available capacity.
So Answer B and E are correct:
Re-configure the load-testing software to re-resolve DNS for each web request.
Configure ELB session stickiness to use the app-specific session cookie.
Launch and run the load-tester EC2 instance from us-east-1 instead- incorrect– Explanation: Launching the load tester EC2 instance from different region will not change the situation. Because of ELB session stickiness settings, the request will continue to be send to a particular web server until load testing software re-resolve DNS at least once per minute. This issue only happens in testing env.
Use a 3rd-party load-testing service which offers globally-distributed test clients- Not the best recommendation.
Explanation: This may help to re-distribute the traffic to all 4 web servers. But, this recommendation heavily depends upon the software that will be used instead of the one currently used. We always choose the best answer in exam so will rule out out this option as we have better option available.
Configure ELB and Auto Scaling to distribute across us-west-2a and us-west-2c- Incorrect
Explanation: This will also not solve the problem. Also, us-west-2c is not mentioned in the question.
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Answer: B, C
http://jayendrapatil.com/tag/elb/
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B and E
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