Exam AWS Certified Solutions Architect - Associate SAA-C02 topic 1 question 169 discussion

C. Change the Auto Scaling group to use six servers across three Availability Zones

Needs to run 4 instances at all time. So we need 2 instances each in 3 AZs. So answer is C. Option D also works but it will cost two more instances.

Option C, "Change the Auto Scaling group to use six servers across three Availability Zones," is the most appropriate choice. This configuration spreads the workload across multiple zones, ensuring that even if one Availability Zone fails, the service remains available in other zones, meeting the SLA requirement of a minimum of four instances at all times.

It cannot be A come onnnnn !!!!

The company needs a minimum of "four" instances at all times to meet the required service level agreement (SLA) while keeping costs low. If an Availability Zone fails, how can the company !remain compliant with the SLA!? so ans simple > "D"

C and D are good for minimum 4 instances running all the time but only C is correct cuz C is cheaper than D. 6 server in 3 AZ so 2 server in each AZ so 4 min is still okay if one AZ goes down.

Target Tracking – scale based on target value for a specific CloudWatch metric, not number of instances.

will go with C

Having more instances in two AZs wont increase SLA. https://docs.aws.amazon.com/wellarchitected/latest/reliability-pillar/example-implementations-for-availability-goals.html

three AZs are more resilient, and is less expensive than 8 instances

Simple rule, 8 servers more expensive than 6, so answer is obvious , C

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We have two requirements we have to meet 1. at least 4 instances should be run at one time 2. keeping expenses low. A - my answer. I would like to see here something like that "keep 4 instances across three Availability Zones". But we have what we have. B - there are no needs to run more powerful instances. C - it increases availability and fault tolerance, however it increases costs, while we can use 4 instances, with answer C we will use 6 instances which mean higher costs. D - less fault tolerance as C but with higher costs.

Costs should be kept low.. D ruled out... No changes need at app level or to others parts of infra as ASG masks this.

A appears wrong as : What is target tracking scaling policy? A target tracking scaling policy assumes that it should scale out your Auto Scaling group when the specified metric is above the target value. You cannot use a target tracking scaling policy to scale out your Auto Scaling group when the specified metric is below the target value. So in theory, if you could scale using a target scaling policy, and the instance count dropped BELOW 4, it can't be used to scale out (add instances) Source: https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-scaling-target-tracking.html B: Is irrelevant as its not the size that counts C wins as this will leave 4 instances online if one availability zone fails at a lower cost that D D looses as this will leave 4 instances running even if an availability zone fails but at a higher cost to C.

The two key requirement are multi AZ and minimum of 4 instances. To achieve this you need to increase both the AZ and instance count. 3 AZ allows for one fail AZ, which will leave 2 AZ online with 4 instances assuming 2 instances in each AZ.

- Fault tolerant: 4 instances each AZ. Each of one down, there are already 4 instances up. - SLA: At least 4 instances. It might be down some AZ. SLA preserve at least 99.99% uptime. Question mentioned low cost. This means 2 instances could be create when an AZ down. I opted A.