Add autoscaling rules

Author: Steven Nemetz

autoscaling-rules.tf

@@ -0,0 +1,54 @@
+
+// CloudWatch Alarms
+resource "aws_cloudwatch_metric_alarm" "high_cpu" {
+  count = "${var.enable_scaling_policies}"
+  alarm_name          = "${title("ec2-asg-${var.name}-high-cpu-utilization")}"
+  comparison_operator = "GreaterThanOrEqualToThreshold"
+  evaluation_periods  = "${var.scaling_policy_high_cpu_evaluation_periods}"
+  metric_name         = "CPUUtilization"
+  namespace           = "AWS/EC2"
+  period              = "${var.scaling_policy_high_cpu_period}"
+  statistic           = "Average"
+  threshold           = "${var.scaling_policy_high_cpu_threshold}"
+  alarm_description = "This metric monitor ec2 high cpu utilization"
+  alarm_actions     = ["${aws_autoscaling_policy.cpu_scaling_out.arn}"]
+  dimensions {
+    AutoScalingGroupName = "${aws_autoscaling_group.this.name}"
+  }
+}
+
+resource "aws_cloudwatch_metric_alarm" "low_cpu" {
+  count = "${var.enable_scaling_policies}"
+  alarm_name          = "${title("ec2-asg-${var.name}-low-cpu-utilization")}"
+  comparison_operator = "LessThanThreshold"
+  evaluation_periods  = "${var.scaling_policy_low_cpu_evaluation_periods}"
+  metric_name         = "CPUUtilization"
+  namespace           = "AWS/EC2"
+  period              = "${var.scaling_policy_low_cpu_period}"
+  statistic           = "Average"
+  threshold           = "${var.scaling_policy_low_cpu_threshold}"
+  alarm_description = "This metric monitor ec2 low cpu utilization"
+  alarm_actions     = ["${aws_autoscaling_policy.cpu_scaling_in.arn}"]
+  dimensions {
+    AutoScalingGroupName = "${aws_autoscaling_group.this.name}"
+  }
+}
+
+// Auto Scaling Policy
+resource "aws_autoscaling_policy" "cpu_scaling_out" {
+  count = "${var.enable_scaling_policies}"
+  name                   = "cpu-scaling-out"
+  scaling_adjustment     = "${length(var.vpc_zone_identifier)}"
+  adjustment_type        = "ChangeInCapacity"
+  cooldown               = "${var.scaling_policy_scaling_out_cooldown}"
+  autoscaling_group_name = "${aws_autoscaling_group.this.name}"
+}
+
+resource "aws_autoscaling_policy" "cpu_scaling_in" {
+  count = "${var.enable_scaling_policies}"
+  name                   = "cpu-scaling-in"
+  scaling_adjustment     = -1
+  adjustment_type        = "ChangeInCapacity"
+  cooldown               = "${var.scaling_policy_scaling_in_cooldown}"
+  autoscaling_group_name = "${aws_autoscaling_group.this.name}"
+}

main.tf

@@ -86,7 +86,7 @@ resource "aws_autoscaling_group" "this" {
   count = "${module.enabled.value}"
 
   name_prefix          = "${coalesce(var.asg_name, module.label.id)}-"
-  launch_configuration = "${var.launch_configuration == "" ? element(aws_launch_configuration.this.*.name, 0) : var.launch_configuration}"
+  launch_configuration = "${var.launch_configuration == "" ? element(concat(aws_launch_configuration.this.*.name, list("")), 0) : var.launch_configuration}"
   vpc_zone_identifier  = ["${var.vpc_zone_identifier}"]
   max_size             = "${var.max_size}"
   min_size             = "${var.min_size}"

variables.tf

@@ -240,3 +240,49 @@ variable "wait_for_elb_capacity" {
   description = "Setting this will cause Terraform to wait for exactly this number of healthy instances in all attached load balancers on both create and update operations. Takes precedence over min_elb_capacity behavior."
   default     = false
 }
+
+// Autoscaling rules
+variable "enable_scaling_policies" {
+  description = "Enable default scale-in and scale-out policies based on CPU Utilization"
+  default     = false
+}
+
+variable "scaling_policy_high_cpu_evaluation_periods" {
+  description = "The number of periods over which data is compared to the specified threshold"
+  default     = 5
+}
+
+variable "scaling_policy_high_cpu_period" {
+  description = "The period in seconds over which the specified statistic is applied"
+  default     = 60
+}
+
+variable "scaling_policy_high_cpu_threshold" {
+  description = "The value against which the specified statistic is compared"
+  default     = 60
+}
+
+variable "scaling_policy_scaling_out_cooldown" {
+  description = "The amount of time, in seconds, after a scaling activity completes and before the next scaling activity can start"
+  default     = 300
+}
+
+variable "scaling_policy_low_cpu_evaluation_periods" {
+  description = "The number of periods over which data is compared to the specified threshold"
+  default     = 3
+}
+
+variable "scaling_policy_low_cpu_period" {
+  description = "The period in seconds over which the specified statistic is applied"
+  default     = 900
+}
+
+variable "scaling_policy_low_cpu_threshold" {
+  description = "The value against which the specified statistic is compared"
+  default     = 20
+}
+
+variable "scaling_policy_scaling_in_cooldown" {
+  description = "The amount of time, in seconds, after a scaling activity completes and before the next scaling activity can start"
+  default     = 3000
+}