Skip to content

07_ASG.md

Latest commit

 

History

History
86 lines (62 loc) · 2.62 KB

07_ASG.md

File metadata and controls

86 lines (62 loc) · 2.62 KB
Raw

Auto Scaling Group (ASG)

Overview

  • In real life, the load on your websites and applications can change
  • In the cloud, you can create and get rid of servers very quickly
  • ASG are free (you only pay for the underlying EC2 instances)

The Goal of an Auto Scaling Group (ASG):

  • Scale out (add EC2 instances) to match an increased load
  • Scale in (remove EC2 instances) to match a decreased load
  • Ensure we have a minimum and 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 (e.g., if unhealthy)

Auto Scaling Group Attributes

An ASG requires a Launch Template (older "Launch Configurations" are deprecated):

  • AMI + Instance Type
  • EC2 User Data
  • EBS Volumes
  • Security Groups
  • SSH Key Pair
  • IAM Roles for your EC2 Instances
  • Network + Subnets Information
  • Load Balancer Information
  • Min Size / Max Size / Initial Capacity
  • Scaling Policies

Auto Scaling — CloudWatch Alarms & Scaling

  • It is possible to scale an ASG based on CloudWatch alarms
  • An alarm monitors a metric (such as Average CPU, or a custom metric)
  • Metrics 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 Groups — Scaling Policies

1. 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 (e.g., CPU > 70%), then add 2 units
  • When a CloudWatch alarm is triggered (e.g., CPU < 30%), then remove 1

2. Scheduled Scaling

  • Anticipate scaling based on known usage patterns
  • Example: increase the min capacity to 10 at 5 pm on Fridays

3. Predictive Scaling

  • Continuously forecast load and schedule scaling ahead

Good Metrics to Scale On

Metric Description
CPUUtilization Average CPU utilization across your instances
RequestCountPerTarget To make sure the number of requests per EC2 instance is stable
Average Network In / Out If your application is network bound
Any custom metric That you push using CloudWatch

ASG Soft Limits

Resource Limit
Auto Scaling Groups per region 200
Launch Configurations per region 1,000
Launch Templates per region 1,000
Scaling Policies per Auto Scaling Group 50