Description:
Amazon Lightsail offers instances that provide a baseline amount of CPU performance, but also have the ability to temporarily provide additional CPU performance above the baseline as needed. This is referred to as bursting.
Rational:
You can configure Lightsail to notify you when a metric for one of your instances CPU utilization crosses a specified threshold. Notifications can be in the form of a banner displayed in the Lightsail console, an email sent to an address you specify or an SMS text message sent to a mobile phone number you specify.
Impact:
If the alarm threshold is breached you will receive a notification in the Lightsail console, and, optionally, you can choose to receive an email message and/or SMS message.
Default Value:
By default, lightsail will not set any alarm.
Audit:
- Sign in to AWS Management console 
- Go to the Lightsail service at https://lightsail.aws.amazon.com/ 
- Choose and click on the instance you want to examine 
- Go to the Metrics tab and select CPU utilization in the drop-down menu 
- In the bottom check whether is there any alarm configured or not  
Remediation:
Pre-requisites:
- Sign in as admin or IAM user with required permissions 
Implementation steps:
- Sign in to AWS Management console 
- Go to the Lightsail service at https://lightsail.aws.amazon.com/ 
- Choose and click on the instance you want to set the alarm 
- Go to the Metrics tab and select CPU utilization in the drop-down menu 
- Click on the CPU utilization  
- Click on Add Alarm at the bottom  
- Set the mathematical expression and threshold along with the monitoring frequency as per your requirement  
- Choose the notifying option from the list of options available  
- Click on create 
Via CLI:
put-alarm
--alarm-name <value>
--metric-name <value>
--monitored-resource-name <value>
--comparison-operator <value>
--threshold <value>
--evaluation-periods <value>
[--datapoints-to-alarm <value>]
[--treat-missing-data <value>]
[--contact-protocols <value>]
[--notification-triggers <value>
Backout plan:
- Sign in to AWS Management console 
- Go to the Lightsail service at https://lightsail.aws.amazon.com/ 
- Choose and click on the instance you want to disable the alarm 
- Go to the Metrics tab and select CPU utilization in the drop-down menu 
- At bottom Click on toggle button to disable the alarm or click on the side menu and select Delete Alarm to delete the alarm  
Reference:
https://lightsail.aws.amazon.com/ls/docs/en_us/articles/amazon-lightsail-notifications
