AWS Certified Solutions Architect - Associate
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A company runs a stateful production application on Amazon EC2 instances. The application requires at least two EC2 instances to always be running.
A solutions architect needs to design a highly available and fault-tolerant architecture for the application. The solutions architect creates an Auto Scaling group of EC2 instances.
Which set of additional steps should the solutions architect take to meet these requirements?
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A
Set the Auto Scaling group's minimum capacity to two. Deploy one On-Demand Instance in one Availability Zone and one On-Demand Instance in a second Availability Zone.
B
Set the Auto Scaling group's minimum capacity to four. Deploy two On-Demand Instances in one Availability Zone and two On-Demand Instances in a second Availability Zone.
C
Set the Auto Scaling group's minimum capacity to two. Deploy four Spot Instances in one Availability Zone.
D
Set the Auto Scaling group's minimum capacity to four. Deploy two On-Demand Instances in one Availability Zone and two Spot Instances in a second Availability Zone.
Explanation:
Explanation
Correct Answer: A
Why Option A is correct:
- Minimum capacity of two - The requirement states that at least two EC2 instances must always be running. Setting the minimum capacity to two ensures that the Auto Scaling group will always maintain at least two instances.
- Distribution across Availability Zones - Deploying one instance in one AZ and another instance in a second AZ provides high availability and fault tolerance. If one Availability Zone fails, the application will still have one instance running in the other AZ.
- On-Demand Instances - For production stateful applications that require guaranteed availability, On-Demand Instances are appropriate as they are not subject to interruption like Spot Instances.
Why other options are incorrect:
Option B: Setting minimum capacity to four is unnecessary and wasteful since the requirement is only for two instances. While distributing across AZs is good, having four instances when only two are required doesn't align with cost optimization principles.
Option C: Using Spot Instances for a production stateful application that requires guaranteed availability is inappropriate. Spot Instances can be interrupted with little notice. Additionally, deploying all instances in a single Availability Zone creates a single point of failure.
Option D: While distributing across AZs is good, mixing On-Demand and Spot Instances for a production stateful application is not ideal. The Spot Instances could be interrupted, potentially leaving only two instances running (or fewer if one fails), which might violate the "at least two always running" requirement. Also, having four instances when only two are required is unnecessary.
Key AWS Concepts:
- Auto Scaling Groups help maintain the desired number of instances
- Multi-AZ deployment provides high availability and fault tolerance
- On-Demand Instances provide guaranteed availability for production workloads
- Spot Instances are cost-effective but can be interrupted, making them unsuitable for critical production applications that require guaranteed availability
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