ASG - Auto Scaling Group

Question 1

What does an ASG define regarding capacity?

Answer 1

defines a min, max and initial capacity of machines running

Question 2

How are ASGs related to ELBs?

Answer 2

an ASGs automatically scales out or in instances to a load balancer

Question 3

What can you use to create an ASG?

Answer 3

A launch template (newer and recommended) or a launch configuration or an EC2 instance

Question 4

Based on what an ASG scale?

Answer 4

It can scale based on

• scaling policies
• CloudWatch alarms created from custom metrics sent
• based on a schedule

Question 5

What you need to do to update an ASG?

Answer 5

u need to provide a new launch template / configuration

Question 6

What happens to IAM roles attached to an ASG?

Answer 6

will get assigned to EC2 instances

Question 7

What actions can be taken by an ASG if an ELB marks an instance as unhealthy

Answer 7

the ASG can terminate the unhealthy instance and hence replace it

Question 8

Which are the ASG scaling policies?

Answer 8

• Target Tracking Scaling
• Simple / Step Scaling
• Scheduled Actions

Question 9

Mention the Target Tracking Scaling policy concept

Answer 9

you want to keep something stable like:

avg ASG CPU to stay around 40%

Question 10

Mention the ASG Simple / Step Scaling policy concept

Answer 10

you set max or min metric values to achieve like:
• When a CloudWatch alarm is triggered (example CPU > 70%), then add 2 units
• When a CloudWatch alarm is triggered (example CPU < 30%), then remove 1

Question 11

What is the ASG Scaling Cooldown?

Answer 11

The cooldown period helps to ensure that your Auto Scaling group doesn’t launch or terminate additional instances before the previous scaling activity takes effect.

Question 12

Can you define an ASG scaling cooldown?

Answer 12

yes, in addition to default cooldown, you can create cooldowns that apply to specific simple scaling policies

Question 13

What is the default ASG default cooldown period?

Answer 13

5 minutes

Question 14

What is the ASG Default Termination Policy?

Answer 14

1. Find the AZ which has the most number of instances
2. Delete the one with the oldest launch configuration
3. Delete the one closest to the end of the billing period
   • ASG tries the balance the number of instances across AZ by default

Question 15

What does ASG Lifecycle Hooks allow you to do?

Answer 15

to perform extra steps before the instance goes in service (Pending state) and before the instance is terminated (Terminating state)

Question 16

What is included in the ASG launch template / configuration?

Answer 16

Basically everything included in an EC2 instance:
- AMI
- instance type
- key-pair
- SGs
...etc

Question 17

What is the main difference between ASG launch configuration and ASG launch templates

Answer 17

configuration is legacy and must be re-created every time.

template can have multiplle versions and is recommended by AWS going forward.

Question 18

How are metrics computed in ASGs?

Answer 18

for the overall ASG instances

Question 19

Who can terminate and replace instances marked as unhealthy? The ASG or the ALB?

Answer 19

ASG

Question 20

What is the difference between Step and Simple scaling?

Answer 20

• Step scaling: based on a set of scaling adjustments, known as step adjustments, that vary based on the size of the alarm breach.
• Simple scaling: based on a single scaling adjustment.