Auto scaling Alarms

• It is possible to scale an ASG( Auto Scaling Group) based on CloudWatch alarms
• An Alarm monitors a metric(such as Average CPU).
• Metrics are computed for the overall ASG instances.
• Based on the alarm:

1. we can create scale-out policies (increase the number of instances).
2. we can create scale-in policies (decrease the number of instances)

           

This post will hands-on for:

1. Create CPU alarm for our ASG.
2. Trigger above CPU alarm.

Let's get hands dirty:

Scale in:

• Navigate to Auto scaling groups page --> scaling policies -->Add policy.

• Click on Create a simple scaling policy.

    

• Now click on Create new alarm.

Here i am provide inputs to get alarm, if the CPU utilization is above 50%,for at least 1 of 5 minutes.

Name of alarm is just description & Finally click on Create Alarm.

Conformation screen.

Automation:

Provide Name field info.

Take the action: here i'm add 2 instances if the alarm is triggered.(when ever the alarm triggered)

wait time: 60 sec

Finally click on create.

similarly we can create new alarm for scale out. here i am consider if the cpu utilization is less then 10 %. Remove 1 EC2 instance automatically.