Fault Tolerant Deployments for us-west-2 AWS Region

Answer - D and E.

Option D- US West 2a-6 , US West 2b - 6, US West 2c-0

If US West 2a goes down, we will still have 6 instances running in US West 2b.

If US West 2b goes down, we will still have 6 instances running in US West 2a.

If US West 2c goes down, we will still have 6 instances running in US West 2a, 6 instances running in US West 2b.

Option E- US West 2a-3 , US West 2b - 3, US West 2c-3

If US West 2a goes down, we will still have 3 instances running in US West 2b and 3 instances running in US West 2c.

If US West 2b goes down, we will still have 3 instances running in US West 2a and 3 instances running in US West 2c.

If US West 2c goes down, we will still have 3 instances running in US West 2a and 3 instances running in US West 2b.

Option A is incorrect because, even if one AZ becomes unavailable, we will only have 4 instances available.

This does not meet the specified requirements.

Option B is incorrect because, when either us-west-2a or us-west-2b is unavailable, you would only have 3 instances available.

This does not meet the specified requirements.

Option C is incorrect because, if us-west-2a becomes unavailable, you would only have 4 instances available.

This also does not meet the specified requirements.

For more information on AWS Regions and Availability Zones, please visit the following URL:

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Concepts.RegionsAndAvailabilityZones.html

Note:

In this scenario, we need to have 6 instances running all the time, even when 1 AZ is down.

Hence options D & E are correct.

Sure, I'd be happy to help you understand the answer to this question.

The question is asking which of the given deployments provides fault tolerance if one availability zone in us-west-2 becomes unavailable, while also ensuring that 6 EC2 instances are running at all times.

To understand the answer, it's important to first understand what an availability zone is in AWS. An availability zone (AZ) is a data center in a specific geographic region that is isolated from other AZs in terms of power, cooling, and network connectivity. This isolation helps ensure that if there is an issue in one AZ, it does not affect the other AZs in the region.

Now, let's look at each of the answer options:

A. 2 EC2 Instances in us-west-2a, 2 EC2 Instances in us-west-2b, and 2 EC2 Instances in us-west-2c This deployment spreads the EC2 instances evenly across all three availability zones. However, if one AZ becomes unavailable, there will only be 4 EC2 instances remaining, which is not enough to meet the requirement of 6 EC2 instances running at all times. Therefore, this option is not a correct answer.

B. 3 EC2 Instances in us-west-2a, 3 EC2 Instances in us-west-2b, and no EC2 Instances in us-west-2c This deployment puts all 6 EC2 instances in two availability zones, us-west-2a and us-west-2b, and does not use the third availability zone, us-west-2c. If one of these two AZs becomes unavailable, there will still be 3 EC2 instances running in the other AZ, which meets the requirement of having at least 6 EC2 instances running at all times. This option provides fault tolerance and is therefore a correct answer.

C. 4 EC2 Instances in us-west-2a, 2 EC2 Instances in us-west-2b, and 2 EC2 Instances in us-west-2c This deployment puts the majority of the EC2 instances in us-west-2a, with 4 instances, and splits the remaining 2 instances across the other two AZs. If us-west-2a becomes unavailable, there will only be 4 EC2 instances remaining across the other two AZs, which is not enough to meet the requirement of 6 EC2 instances running at all times. Therefore, this option is not a correct answer.

D. 6 EC2 Instances in us-west-2a, 6 EC2 Instances in us-west-2b, and no EC2 Instances in us-west-2c This deployment puts all 12 EC2 instances in two AZs, us-west-2a and us-west-2b, and does not use the third AZ, us-west-2c. Similar to option B, if one of these two AZs becomes unavailable, there will still be 6 EC2 instances running in the other AZ, which meets the requirement of having at least 6 EC2 instances running at all times. However, this option uses more resources than necessary, with 12 EC2 instances running instead of the required 6, and is therefore not a practical solution.

E. 3 EC2 Instances in us-west-2a, 3 EC2 Instances in us-west-2b, and 3 EC2 Instances in us-west-2c. This deployment evenly distributes the EC2 instances across all three availability zones. However, if one AZ becomes unavailable, there will only be 2 EC2 instances running in each of the remaining AZs, which is not enough to meet the requirement of 6 EC2 instances running at all times.