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Exam ANS-C00 topic 1 question 91 discussion

Exam question from Amazon's ANS-C00

Question #: 91
Topic #: 1

An organization is migrating its on-premises applications to AWS by using a lift-and-shift approach, taking advantage of managed AWS services wherever possible. The company must be able to edit the application code during the migration phase. One application is a traditional three-tier application, consisting of a web presentation tier, an application tier, and a database tier. The external calling client applications need their sessions to remain sticky to both the web and application nodes that they initially connect to.
Which load balancing solution would allow the web and application tiers to scale horizontally independent from one another other?

A. Use an Application Load Balancer at the web tier and a Classic Load Balancer at the application tier. Set session stickiness on both, but update the application code to create an application-controlled cookie on the Classic Load Balancer.
B. Use an Application Load Balancer at both the web and application tiers, setting session stickiness at the target group level for both tiers.
C. Deploy a web node and an application node as separate containers on the same host, using task linking to create a relationship between the pair. Add an Application Load Balancer with session stickiness in front of all web node containers.
D. Use a Network Load Balancer at the web tier, and an Application Load Balancer at the application tier. Enable session stickiness on the Application Load Balancer, but take advantage of the native WebSockets protocols available to the Network Load Balancer.

Show Suggested Answer

Suggested Answer: B 🗳️

by exmjame at May 12, 2020, 12:19 p.m.

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inf

Highly Voted 3 years, 7 months ago

Answer: A A - correct - sticky ALB + sticky CLB + cookie. Also caters for non-web based app tier given its a traditional 3-tier app. App must be editable (e.g. to include a cookie) B - incorrect - traditional app tier, unlikely to use HTTP/HTTPS, which can't sit behind an ALB C - incorrect - can't scale horizontally independent of each other. D - incorrect - NLBs maintain the same target for the "life of the connection", unlike cookies which persist. Also, no idea if app tier is web based, could be TCP

upvoted 12 times

droop72

3 years, 7 months ago

https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#sticky-session The reason to scratch B maybe: If you are using multiple layers of Application Load Balancers, you can enable sticky sessions on one layer only, because the load balancers would use the same cookie name.

upvoted 4 times

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jerac58653

3 years ago

I am not a developer but as they say "including a web display layer", I would assume we are talking here about an web app. Why would otherwise have a web layer if you do not have web application. And if it is web application, it is using HTTP/HTTPs, so ALB is possible. As somebody mentioned, application-based cookies should work independently with 2 ALBs. A seems also possible but more difficult to realize.

upvoted 2 times

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eeghai7thioyaiR4

Highly Voted 3 years, 7 months ago

In that architecture, you have a tier serving HTML/JS, a tier serving some kind of API, and a database tier So clients connects to both the first two tiers, directly The right answer is B ALB stickyness uses a cookie called AWSALBAPP by default, to map a customer to a backend, across requests However, according to the doc (https://docs.aws.amazon.com/fr_fr/elasticloadbalancing/latest/application/sticky-sessions.html), you can rename that cookie to avoid collision So, in our design, nothing prevent us from using a couple of ALB This is also the cleanest option .. maybe A will work, but come on, creating a CLB, changing application code to create a specific cookie .. ? That is an aweful solution TLDR: answer B

upvoted 7 times

sapien45

3 years, 2 months ago

I agree, really, recommending to use a CLB when every single AWS document recommends to get away from it ? B, clear and simple

upvoted 2 times

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hello_aws

Most Recent 2 years, 9 months ago

Selected Answer: A

A, agree with droop72

upvoted 1 times

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NSF2

3 years, 6 months ago

I would go for B “If you are using multiple layers of Application Load Balancers, you can enable sticky sessions across all layers with application-based cookies. However, with duration-based cookies, you can enable sticky sessions only on one layer, because AWSALB is the only name available.” https://docs.aws.amazon.com/elasticloadbalancing/latest/application/sticky-sessions.html

upvoted 4 times

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Johnny_Green

3 years, 7 months ago

For ALB sticky sessions: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#sticky-sessions Regarding sticky sessions for Classic Load Balancer: https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-sticky-sessions.html Sessions for Network Load Balancer are inherently sticky due to the flow hashing algorithm used. Based on the above and the following statement: "If you are using multiple layers of Application Load Balancers, you can enable sticky sessions on one layer only, because the load balancers would use the same cookie name.", it appears that Answer D is correct.

upvoted 1 times

Johnny_Green

3 years, 7 months ago

Here is another reference that shows such combination (NLB + ALB) can leverage the benefits of both by putting an Application Load Balancer behind a Network Load Balancer. https://aws.amazon.com/blogs/networking-and-content-delivery/using-static-ip-addresses-for-application-load-balancers/

upvoted 1 times

Johnny_Green

3 years, 7 months ago

Reconsideration suggests that A is the correct answer because of the following requirements: 1) taking advantage of managed AWS services wherever possible; 2) must be able to edit the application code during the migration phase; 3) application is a traditional three-tier application.

upvoted 1 times

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3 years, 8 months ago

ALB target group stickyness; https://aws.amazon.com/blogs/aws/new-application-load-balancer-simplifies-deployment-with-weighted-target-groups/

upvoted 1 times

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