Setup Auto Scaling along with scale up and down policy

aws asg terrafrom sample.txt

Setup Auto Scaling along with scale up and down policy

1. Build AMI
	we need to first build AMI by installing Amazon monitoring scripts to monitor memory utilization and send to cloudwathc and also install other required dependencies to run application.

2. Create launch configuration
	we create launch configuration with options like availability zone, security groups, vpc, etc.

3. Create autoscaling group and autoscaling policy
	This points at our earlier launch configuration and it lauch instances based on launch configuration. The tag,vpc security groups is propogated to any launched instance at launch. Also we define min and max number of instances.

	In autoscaling policy we define metric type like Average CPU and Memory utilization based on clodwatch metrics.

	In autoscaling group we also define load balacer and target group to attach launched instances.


Below is ths sample Terraform code for Auto Scaling Groups

resource "aws_launch_configuration" "demo-lc" {
    name     = "demo-lc"
    image_id = <AMI ID>
    instance_type = <instance type>
    user_data = file("init-script.sh")

    root_block_device {
        volume_type = "gp2"
        volume_size = "50"
    }
}

resource "aws_autoscaling_group" "demo-asg" {
    availability_zones = ["ap-south-1"]
    name = "demo-asg"
    max_size = "20"
    min_size = "1"
    health_check_grace_period = 300
    health_check_type = "EC2"
    desired_capacity = 2
    force_delete = true
    launch_configuration = "${aws_launch_configuration.demo-lc.name}"
}

resource "aws_autoscaling_policy" "agents-scale-up" {
    name = "agents-scale-up"
    scaling_adjustment = 1
    adjustment_type = "ChangeInCapacity"
    cooldown = 300
    autoscaling_group_name = "${aws_autoscaling_group.demo-asg.name}"
}

resource "aws_autoscaling_policy" "agents-scale-down" {
    name = "agents-scale-down"
    scaling_adjustment = -1
    adjustment_type = "ChangeInCapacity"
    cooldown = 300
    autoscaling_group_name = "${aws_autoscaling_group.demo-asg.name}"
}

resource "aws_cloudwatch_metric_alarm" "memory-high" {
    alarm_name = "mem-util-high-agents"
    comparison_operator = "GreaterThanOrEqualToThreshold"
    evaluation_periods = "2"
    metric_name = "MemoryUtilization"
    namespace = "System/Linux"
    period = "300"
    statistic = "Average"
    threshold = "80"
    alarm_description = "This metric monitors ec2 memory for high utilization on agent hosts"
    alarm_actions = [
        "${aws_autoscaling_policy.agents-scale-up.arn}"
    ]
    dimensions = {
        AutoScalingGroupName = "${aws_autoscaling_group.demo-asg.name}"
    }
}

resource "aws_cloudwatch_metric_alarm" "memory-low" {
    alarm_name = "mem-util-low-agents"
    comparison_operator = "LessThanOrEqualToThreshold"
    evaluation_periods = "2"
    metric_name = "MemoryUtilization"
    namespace = "System/Linux"
    period = "300"
    statistic = "Average"
    threshold = "40"
    alarm_description = "This metric monitors ec2 memory for low utilization on agent hosts"
    alarm_actions = [
        "${aws_autoscaling_policy.agents-scale-down.arn}"
    ]
    dimensions = {
        AutoScalingGroupName = "${aws_autoscaling_group.demo-asg.name}"
    }
}