High Availability

Question 1

What are optimal CPU Utilization percentage to scale out and in?

Answer 1

Scale out @ 80% , Scale in @ 40%

Question 2

What is required before creating ASG?

Answer 2

Launch configuration.
note that ELB is not required!

Question 3

What is the name of the ‘set of instructions’ sent from CloudWatch to ASG?

Answer 3

Policy

Question 4

What is Predictive Scaling? And how much data it needs?

Answer 4

It auto-scales based on daily/weekly patterns.
It needs at least 2 weeks of data.

Question 5

What are some valid states for RDS instances?

Answer 5

Pending / In-Service are valid states.
XACTiVEX is not a valid state

Question 6

versioned launch configuration?

Answer 6

Launch template

Question 7

If you changed EC2 settings, How to update the Launch configurations?

Answer 7

Use the EC2 as a template. (do not create manually a new launch configuration)

Question 8

How long can SQS messages be kept?

Answer 8

14 days

Question 9

What would happen to inactive SQS queues?

Answer 9

AWS has right to delete them after 30 days

Question 10

What can be used to subscribe to SNS topics?

Answer 10

Lambda, SQS, email, SMS, HTTP/S

Question 11

What does it mean to make an application ‘stateless’?

Answer 11

Save session data using services as DynamoDB or ElastiCache.

Question 12

How to use a Lambda function on other regions?

Answer 12

A new copy is required.

Question 13

How to build subnets with HA for 3-tier applications?

Answer 13

Create 2 subnets per tier.
& Choose different AZ for each subnet.