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Exam AWS-SysOps topic 1 question 713 discussion

Exam question from Amazon's AWS-SysOps

Question #: 713
Topic #: 1

A SysOps Administrator created an Application Load balancer (ALB) and placed two Amazon EC2 instances in the same subnet behind the ALB. During monitoring, the Administrator observes HealthyHostCount drop to 1 in Amazon CloudWatch.
What is MOST likely causing this issue?

A. The EC2 instances are in the same Availability Zone, causing contention between the two.
B. The route tables are not updated to allow traffic to flow between the ALB and the EC2 instances.
C. The ALB health check has failed, and the ALB has taken EC2 instances out of service.
D. The Amazon Route 53 health check has failed, and the ALB has taken EC2 instances out of service.

Show Suggested Answer

Suggested Answer: A 🗳️

by usmanbaigmughal at Nov. 25, 2019, 6:37 p.m.

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Comments

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albert_kuo

11 months, 3 weeks ago

Selected Answer: C

The HealthyHostCount metric in Amazon CloudWatch measures the number of EC2 instances behind an Application Load Balancer (ALB) that are currently considered healthy by the ALB's health check. If the HealthyHostCount drops to 1, it indicates that only one EC2 instance is passing the health check and considered healthy by the ALB.

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szhang2004

1 year, 5 months ago

Per following link. the correct answer should be A. https://stackoverflow.com/questions/11608888/how-do-i-use-elbs-healthyhostcount-for-monitoring-in-cloudwatch

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antthomas

2 years, 5 months ago

Selected Answer: C

I vote C. https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-troubleshooting.html

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RicardoD

2 years, 8 months ago

C is the answer It is more likely that the ALB health check has failed

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sasquatchshrimp

2 years, 8 months ago

ALB requires 2 subnets, Answer would have to be A. https://acloud.guru/forums/aws-csa-2019/discussion/-LrYbedX1115Pd7z40rq/Why%20does%20an%20ALB%20require%202%20subnets%3F%20Is%20it%20only%20to%20deploy%20itself%3F

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abhishek_m_86

2 years, 8 months ago

C. The ALB health check has failed, and the ALB has taken EC2 instances out of service. Seems right

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jackdryan

2 years, 8 months ago

I'll go with C

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MFDOOM

2 years, 8 months ago

C. The ALB health check has failed, and the ALB has taken EC2 instances out of service.

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Thabo_Ramoshai

2 years, 8 months ago

C. The ALB health check has failed, and the ALB has taken EC2 instances out of service. According to the description here BOTH instances were taken out of service, which is not true as on 1 instance was deregistered. I would go for C, but both instances cannot be deregistered from what the admin observed. Ans is A

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waterzhong

2 years, 8 months ago

Answer C.

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JGD

2 years, 8 months ago

Answer C. ALB found one of the target (Ec2 instance) failure and that's a reason where the Instance is Out of Service.So, the CloudWatch will show only 1 healthyhostcount.

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AWS_Noob

2 years, 8 months ago

C is correct

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a_w_s

2 years, 8 months ago

A : is for me the good answer! HEALTHYHOSTCOUNT is the number of healthy instances registered, so the 2 EC2 instances are in the same subnet it means the same AZ (1subnet = 1 AZ)

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a_w_s

2 years, 8 months ago

Sorry! C is the good answer! The health check of 1 instance is bad...

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Kot

2 years, 8 months ago

How two EC2 instances in one subnet behind the ALB cloud causing contention between each other. And drop the healthcheck metric by this reason. No one troubleshooting practice mentions this case. But a lot of cases for fail helthcheck of ALB in one or different AZs and different target groups which ALB balances are presets in documentation. And it coulb be not EC2 faildown only. So I vote C. https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-troubleshooting.html

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awsnoob

2 years, 9 months ago

I think is C, the question did not mentioned that cross zone load balancing...

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white_shadow

2 years, 9 months ago

Why not A? If the HealthyHostCount default value on average, that A should be correct https://forums.aws.amazon.com/message.jspa?messageID=527754 https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-cloudwatch-metrics.html

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white_shadow

2 years, 9 months ago

Also for C, it says ALB health check failed, not the EC2. also mentions "EC2 instances out of service" not one, so even if this is true, it will take both instances not one.

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karmaah

2 years, 9 months ago

Thanks white_shadown to make me to review the ans again. Looks Ans A is correct. If one of the instance health check failed does not mean that Ec2 server is down. There are N number of reasons including contention or nw or etc..Pl read the below link for the reason of failure HC on ELB. https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/ts-elb-healthcheck.html if ALB's Health Check itself failed then,how will it remove the EC2 Instances out of service since it can not reach the Ec2. However C looks not appropriate correct answer that A.

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karmaah

2 years, 9 months ago

Ans is C

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karmaah

2 years, 9 months ago

Pl ignore and review my updated comment.

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