01 ASG Overview - AWS Study Notes

Terms
Desired capacity or actual size means, number of instance while first time running
Minimum size means number of minimum instance while application load is minimum
Maximum size means number of maximum instance while application load is maximum
Scale Out mean adding instance
Scale In means removing instance
When new AMI is required,
Keep the existing Target Group
Create new Launch Configuration
ASG terminate the instance in the following manner
Select instance with oldest launch config
Select instance with closest billing hour
The more instance in a AZ got terminated first
When we need to manually add or remove instances, update the launch configuration with desired capacity

A launch configuration can not be updated after being created

Ensure the ASG does not add or terminate instance without previous activity being completed
Default cool-down period is 300 sec
Cool Down Period ensures it will not terminate or launch before the last scaling takes place
To reduce the changing of EC2 Instance
Use high cool-down period
Use high threshold value in the Cloudwatch Alarm Metric
Applicable for Simple Scaling Policy

Target Tracking Scaling
Scaling is done based on specific metric value
Example be, want all the CPU average speed 40%. If goes more usage, add instance
Eligible metrics are
- CPU
- Network
- Requests
Step Scaling oe Simple Scaling
Scaling is done based on set of scaling adjustments
Cloudwatch alarm is involved
Example
- If CPU Usage is over 30% add 2 instance
- If CPU usage is over 70% add 5 instance
Schedule Scaling
Based on usage pattern
Example be, use 10 instance on each friday 10AM - 5PM, other time 1 instance
When a new AMI is required to launch to ASG, need to update the ASG Launch Config