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Your company runs a customer facing event registration site This site is built with a 3-tier architecture with web
and application tier servers and a MySQL database The application requires 6 web tier servers and 6
application tier servers for normal operation, but can run on a minimum of 65% server capacity and a single
MySQL database. When deploying this application in a region with three availability zones (AZs) which
architecture provides high availability?

A.
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.

B.
A web tier deployed across 3 AZs with 2 EC2 (Elastic Compute Cloud) instances in each A2 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.

C.
d 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.

D.
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.

Explanation:
http://highscalability.com/blog/2016/1/11/a-beginners-guide-to-scaling-to-11-million-users-on-amazons.html
https://www.airpair.com/aws/posts/building-a-scalable-web-app-on-amazon-web-services-p1

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