Auto Scaling on AWS

Matthew SwainSoftware Engineer @ MassRelevance

What is AWS Auto Scaling?

Auto Scaling is Amazon’s hosted service for automatically launching and terminating EC2

instances.

Why Use Auto Scaling

• Save money by only using instances when you need them.

• Scale to accommodate expected and unexpected loads.

• Replace unhealthy servers with healthy ones.

What Makes Up Auto Scaling

• Launch Configurations

• Auto Scaling Groups

• Scaling Policies

• Cloud Watch Alarms

Launch Configurations

Templates that describe the parameters passed at launch-time to your EC2 instances.

Examples: AMI, instance type (c1.xlarge, m1.small, …), security groups, spot price

Auto Scaling Groups

A set of EC2 instances that run a launch configuration.

Scaling Policies

A template describing actions to run against an Auto Scaling Group.

E.g. Start two instances in the ASG named “webservers”

Cloud Watch Alarms

Triggers that can run Scaling Policies based on Cloud Watch metrics (AWS’s built in monitoring suite).

E.g. Run Scaling Policy “Launch Webservers” when CPU exceeds a certain threshold for 5 minutes.

A Simple Web Application in Five Steps

• Create an AMI

• Setup an Elastic Load Balancer (ELB)

• Create a Launch Configuration

• Create Scaling Policies

• Create Cloud Watch Alarms

Prerequisites

• AWS Account

• A running web application on an EBS backed instance.

• AWS Command Line tool: http://aws.amazon.com/cli/

ZSH Auto-complete!

Build an AMI

aws ec2 create-image \ --instance-id i-12345678 \ --name awesome-image-v1.0

output: ami-12345678

Create a Load Balancer

aws elb create-load-balancer \ --load-balancer-name 'my-lb' \ --listeners Protocol=http,\ LoadBalancerPort=80,\InstanceProtocol=http,\InstancePort=80 \ --availability-zones us-east-1d

Create a Launch Configuration

aws autoscaling create-launch-configuration \ --launch-configuration-name awesome-lc-v1.0 \ --image-id ami-12345678 \ --key-name my-keypair \ --securty-groups default \ --instance-type c1.xlarge

Create an Auto Scaling Group

aws autoscaling create-autoscaling-group \ --auto-scaling-group-name awesome-asg \ --launch-configuration-name awesome-lc-v1.0 \ --min-size 1 \ --max-size 10 \ --desired-capacity 1 \ --default-cooldown 120 \ --availability-zones us-east-1d \ --load-balancer-names my-lb \ --health-check-type EC2

Create Scaling Policies

aws autoscaling put-scaling-policy \ --auto-scaling-group-name awesome-asg \ --policy-name awesome-asg-up \ --scaling-adjustment 1 \ --adjustment-type ChangeInCapacity \ --cooldown 300

>> arn:aws:autoscaling<...>:policyName/awesome-asg-up

Create Scaling Policies

aws autoscaling put-scaling-policy \ --auto-scaling-group-name awesome-asg \ --policy-name awesome-asg-down \ --scaling-adjustment -1 \ --adjustment-type ChangeInCapacity \ --cooldown 300

>> arn:aws:autoscaling<...>:policyName/awesome-asg-down

Create CloudWatch Alarms

aws cloudwatch put-metric-alarm \ --alarm-name awesome-cpu-high \ --metric-name CPUUtilization \ --actions-enabled \ --alarm-actions arn:aws:<...>:policyName/awesome-asg-up \ --namespace "AWS/EC2" \ --statistic Average \ --dimensions Name=AutoScalingGroupName,Value=awesome-asg \ --period 300 \ --evaluation-periods 1 \ --comparison-operator GreaterThanOrEqualToThreshold \ --threshold 60.0

Create CloudWatch Alarms

aws cloudwatch put-metric-alarm \ --alarm-name awesome-cpu-low \ --metric-name CPUUtilization \ --actions-enabled \ --alarm-actions arn:aws<...>policyName/awesome-asg-down \ --namespace "AWS/EC2" \ --statistic Average \ --dimensions Name=AutoScalingGroupName,Value=awesome-asg \ --period 300 \ --evaluation-periods 1 \ --comparison-operator LessThanOrEqualToThreshold \ --threshold 20.0

The AWS CloudWatch Console

The AWS CloudWatch Console

Advanced Usage

• IAM Roles - Allow instances to access protected S3 resources

• UserData Scripts - Small bash startup scripts passed to EC2 instances at boot time.

• Chef - Client-Server Configuration Management

UserData Scripts

#!/bin/bash

role=fsbootstrap=as-bootstrap-s3.shs3cmd_pkg=s3cmd-.tar.gzPATH=$PATH:/usr/local/bin

cd /tmpwget http://some-public-bucket/${s3cmd_pkg}tar -xzf ${s3cmd_pkg}cd `basename ${s3cmd_pkg} '.tar.gz'`python setup.py install

cd /s3cmd --config /dev/null get s3://private-bucket/${bootstrap}chmod 755 ${bootstrap}./${bootstrap} ${role} 2>&1 > ${bootstrap}.out

Questions?Twitter: @mswain