The load balancer market-alb is up, with a listener on 80 forwarding to the target group web-tg, which checks /health. The security group web-sg lets the load balancer in. ~/app.sh installs the shop; building its catalogue takes about two minutes.

1. Keep the latest Amazon Linux image id in AMI, web-sg's id in WEB_SG, web-tg's ARN in TG, and the subnets of us-east-1a and us-east-1b in SUBNET_A and SUBNET_B.

2. A colleague tried to make the launch template web-lt like this, and it failed:

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   aws ec2 create-launch-template --launch-template-name web-lt --launch-template-data "ImageId=$AMI,InstanceType=t3.micro,SecurityGroupIds=$WEB_SG,UserData=$(cat app.sh)"

   Read the error, and create web-lt from app.sh properly.

3. They also wrote the group's command. Run it:

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   aws autoscaling create-auto-scaling-group --auto-scaling-group-name web-asg --launch-template LaunchTemplateName=web-lt,Version='$Latest' --min-size 2 --max-size 4 --desired-capacity 2 --vpc-zone-identifier "$SUBNET_A,$SUBNET_B" --target-group-arns $TG --health-check-type ELB --tags Key=Name,Value=web,PropagateAtLaunch=true

4. Over the next five minutes, list the group's instances and read its scaling activities. Find out why its instances keep being replaced, and fix the group so that a new instance has the time it needs.

5. Once both targets in web-tg are healthy, terminate one of the instances the group lists as InService, and watch the group replace it.