When deploying this application in a region with three availability zones (AZs) which architecture provides high availability?
A web tier deployed across 2 AZs with 3 EC2 (Elastic Compute Cloud) instances in each AZ inside an Auto Scaling Group behind an ELB (elastic load balancer), and an application tier deployed across 2 AZs with 3 EC2 instances in each AZ inside an Auto Scaling Group behind an ELB and one RDS (Relational Database Service) instance deployed with read replicas in the other AZ.
A web tier deployed across 3 AZs with 2 EC2 (Elastic Compute Cloud) instances in each AZ inside an Auto Scaling Group behind an ELB (elastic load balancer) and an application tier deployed across 3 AZs with 2 EC2 instances in each AZ inside an Auto Scaling Group behind an ELB and one RDS (Relational Database Service) Instance deployed with read replicas in the two other AZs.
A web tier deployed across 2 AZs with 3 EC2 (Elastic Compute Cloud) instances in each AZ inside an Auto Scaling Group behind an ELB (elastic load balancer) and an application tier deployed across 2 AZs with 3 EC2 instances m each AZ inside an Auto Scaling Group behind an ELS and a Multi-AZ RDS (Relational Database Service) deployment.
A web tier deployed across 3 AZs with 2 EC2 (Elastic Compute Cloud) instances in each AZ Inside an Auto Scaling Group behind an ELB (elastic load balancer). And an application tier deployed across 3 AZs with 2 EC2 instances in each AZ inside an Auto Scaling Group behind an ELB and a Multi-AZ RDS (Relational Database services) deployment.
Explanations:
This option has the web and application tiers deployed across 2 AZs, which does not meet high availability requirements. Additionally, a single RDS instance with read replicas does not provide sufficient fault tolerance for the database layer.
While this option deploys across 3 AZs, it only provides 2 EC2 instances per AZ for both web and application tiers, which may not meet the minimum requirement of 6 servers.
Although this option correctly deploys the application with sufficient EC2 instances across 2 AZs, it does not fully leverage 3 AZs for high availability. Additionally, a Multi-AZ RDS is used, which is not as fault-tolerant as deploying read replicas in multiple AZs.
This option provides a fully redundant architecture across 3 AZs for both the web and application tiers with sufficient EC2 instances. The Multi-AZ RDS deployment ensures high availability and failover protection for the database.
I classify that the answer is:
A web tier deployed across 3 AZs with 2 EC2 (Elastic Compute Cloud) instances in each AZ Inside an Auto Scaling Group behind an ELB (elastic load balancer). And an application tier deployed across 3 AZs with 2 EC2 instances in each AZ inside an Auto Scaling Group behind an ELB and a Multi-AZ RDS (Relational Database services) deployment.