Auto scaling

If you've applied the patterns and followed the practices enumerated here, you are on the road to success. Unfortunately, success often comes more swiftly than you expect. A mention on Hacker News, Reddit, or Twitter can send waves of traffic your way. Let's take a look at how Amazon's auto scaling feature can help us to meet the demand in a cost effective way. First, we will define a launch configuration for our product—this should go into the instanceAZ1c.tf file:

resource "aws_launch_configuration" "asg_conf" {
  name = "book-asg-config"
  image_id = "ami-001e1c1159ccfe992"
  instance_type = "t2.micro"
}

Then, add an autoscaling group to the same file, which encompasses all AZs, so that the workload gets distributed evenly:

resource "aws_autoscaling_group" "book_group" {
  availability_zones = ["us-east-1a","us-east-1b","us-east-1c"]
  name = "book-group-asg"
  max_size = 5
  min_size = 2
  health_check_grace_period = 300
  health_check_type = "ELB"
  force_delete = true
  launch_configuration = "${aws_launch_configuration.asg_conf.name}"
}

And add a policy that defines the configuration for capacity, causes, adjustment, and cool down, which in this case puts the policy to sleep for an arbitrary five minutes:

resource "aws_autoscaling_policy" "bat" {
  name = "book-policy-ASG"
  scaling_adjustment = 4
  adjustment_type = "ChangeInCapacity"
  cooldown = 300
  autoscaling_group_name = "${aws_autoscaling_group.book_group.name}"
}