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
D 4 – Subnet for each tier in each AZ
http://www.aiotestking.com/amazon/what-is-the-minimum-number-of-subnets-that-need-to-be-configured-in-the-vpc/
answer is D
ELB-
Subnets for Your Load Balancer
To ensure that your load balancer can scale properly, verify that each subnet for your load balancer has a CIDR block with at least a /27 bitmask (for example, 10.0.0.0/27) and has at least 8 free IP addresses. Your load balancer uses these IP addresses to establish connections with the instances.
Create a subnet in each Availability Zone where you want to launch instances. Depending on your application, you can launch your instances in public subnets, private subnets, or a combination of public and private subnets. A public subnet has a route to an Internet gateway. Note that default VPCs have one public subnet per Availability Zone by default.
RDS – https://forums.aws.amazon.com/thread.jspa?threadID=151938
The DB Subnet Group should have at least one subnet in each Availability Zone of the target Region; it identifies the subnets (and the corresponding IP address ranges) where you would like to be able to run DB Instances within the VPC. This will allow future Multi-AZ deployment of RDS to create a new standby in another Availability Zone should the need arise.
You need to do this even for Single-AZ deployments, just in case you want to convert them to Multi-AZ at some point.