Exam AWS Certified Solutions Architect - Associate SAA-C03 topic 1 question 892 discussion

Autoscaling with max=1 is what is needed to keep only one instance at a time - it will still fail, but it will spawn exactly one instance in case of failure (we are not allowed to change the design of the app) Having single instances in different AZ will not help - if one of the AZs is down, the app will still be affected

NOT A: Autoscaling with Maximum of 1 EC2 :D NOT B: Hourly backup... RPO 1hr C: AMI, Multi-AZ -> Fault tolerant NOT D: ECS with Fargate, but it needs to run on EC2..

A has a single point of failure = not fault tolerant

A - Creating an AMI of each application instance ensures that the migrated applications are deployed consistently with their existing configurations, yes, but an Auto Scaling group with a minimum and maximum of one provides no redundancy. If the single instance fails, the application becomes unavailable. B - Backup-based disaster recovery does not provide real-time fault tolerance. It introduces downtime during recovery and does not meet the reliability requirement. C - Launching two EC2 instances in separate Availability Zones (AZs) provides high availability. If one AZ experiences an outage, the application remains accessible on the instance in the other AZ. D - "Changes to the application designs cannot be made."

I will choose Option C for the following reasons: #1 AMI creation: Creating an AMI of each application instance allows for easy replication. #2 Multiple Availability Zones: Launching instances in different Availability Zones provides redundancy in case of regional outages. #3 Network Load Balancer: A Network Load Balancer distributes traffic across the instances, providing high availability by automatically routing requests to a healthy instance if one fails.

What if application is statefull and there's no backup?

I don't see how people can choose A here when it is talking about reliability and the answer only has a maximum of 1. There's nothing about cost effectiveness so there is no reason this one is better. Definitely C.

A. Create an Auto Scaling group that has a minimum of one and a maximum of one. Create an Amazon Machine Image (AMI) of each application instance. Use the AMI to create EC2 instances in the Auto Scaling group Configure an Application Load Balancer in front of the Auto Scaling group.

Fault tolerance is not High Availability Answer A is HA design, not Fault tolerance

A makes sense. C is possible but manual intervention.

answer is A. Auto Scaling Group: Explanation: Minimum and Maximum of one instance: Ensures that the instance is always running. If the instance fails, Auto Scaling will automatically replace it with a new one, maintaining high availability. Amazon Machine Image (AMI): Captures the current state of the application instance, ensuring that new instances launched by Auto Scaling will have the same configuration. Application Load Balancer (ALB): Load Balancer: Distributes traffic to the instances in the Auto Scaling group, ensuring fault tolerance. Even though there is only one instance, the ALB can help manage incoming traffic and be ready for future scaling if needed. For C: While this provides high availability, it does not address fault tolerance as effectively as the Auto Scaling group approach. Without Auto Scaling, if an instance fails, manual intervention is required to launch new instances.

A makes sense

It's either A or B but A is a better option. The application design cannot be changed so we don't know if it can run across 2 servers.

Answer A It is possible to set Min and Max to 1 which will automatically bring up server when it will crash. Taking into consideration that we cannot change application design and load-balancing between regions would probably need that (no information if applications are statefull or stateless) i would go for solution in answer A https://docs.aws.amazon.com/autoscaling/ec2/userguide/asg-capacity-limits.html