What is the minimum number of subnets that need to be c…

A company wants to implement their website in a virtual private cloud (VPC). The web tier will
use an Auto Scaling group across multiple Availability Zones (AZs). The database will use
Multi-AZ RDS MySQL and should not be publicly accessible. ‘What is the minimum number of
subnets that need to be configured in the VPC?

A.
1

B.
2

C.
3

D.
4

Explanation:
Would use VPC with private (DB) and public (WEB) subnets:
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_VPC.Scenarios.html
Multi AZ requirement forces me to multiply subnets by two.
Reasons:
For DB: Your VPC must have at least one subnet in at least two of the Availability Zones in
the region where you want to deploy your DB instance. A subnet is a segment of a VPC’s IP
address range that you can specify and that lets you group instances based on your security
and operational needs
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_VPC.WorkingWithRDSIns
tanceinaVPC.html
For Web: After creating a VPC, you can add one or more subnets in each Availability Zone.
Each subnet must reside entirely within one Availability Zone and cannot span zones
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Subnets.html