What is an Auto Scaling Group?
In real-life, the load of your websites and applications can be change
In the cloud, you can create and get rid of servers very quickly
-
The goal of an Auto Scaling Groups (ASG) is to:
- Scale out (add EC2 intances) to match an increased load
- Scale in (remove EC2 instances) to match a decreased load
- Ensure we have a minimum and a maximum number of EC2 instances running
- Automatically register new instances to a load balancer
- Re-create an EC2 instance in case a previous one is terminated (ex: if unhealthy)
Auto Scaling Group are free - you only pay for the underlying EC2 intances.
Auto Scaling Group Attributes
-
A Launch Template, includes:
- AMI + Instance Type
- EC2 User Data
- EBS Volumes
- Security Groups
- SSH Key Pair
- IAM Role for your EC2 instance
- Network + Subnet Information
- Load Balancer Information
Min Size / Max Size / Initial Capacity
Scaling Policies
CloudWatch Alarm and Scaling
It is posible to scale an ASG based on CloudWatch alarms
An alarm monitors a metric (such as Average CPU, or a custom metric)
Metric such as Average CPU are computed for the overall ASG instances
-
Based on the alarm:
- We can create scale-out policies (increase the number of instances)
- We can create scale-in policies (decrease the number of instances)
Auto Scaling Policies
Dynamic Scaling
-
Target Tracking Scaling
- Simple to set-up
- Example: I want the average ASG CPU to stay at around 40%
-
Simple / Step Scaling
- When a CloudWatch alarm is triggered (ex: CPU > 70%) then add 2 units
- When a CloudWatch alarm is triggerd (ex: CPU < 30%) then remove 1
Scheduled Scaling
- Anticipate a scaling based on known usage patterns
- Example: increase the min capacity to 10 at 5pm on Fridays
Predictive Scaling: continously forecast load and schedule scaling ahead
Good metrics to scale on
CPUUtilization: Average CPU utilization across your instances
RequestCountPerTarget: to make sure the number of requests per EC2 instances is stable
Average Network In/Out (if your application is network bound
Any custom metric (that you push using CloudWatch)
Top comments (0)