Terraform AWS Auto Scaling Module

Module stack supporting multiple deployment scenarios of an Auto Scaling Group to an AWS VPC.

Prerequisites

• Pre-configured AWS VPC

Requirements

• Terraform 0.8.0 or newer
• AWS provider

Group Module

The group module will provision security group, launch template and auto scaling group resources. Both ELB and simple group configurations are supported.

Input Variables

Resource labels

• stack_item_fullname - Long form descriptive name for this stack item. This value is used to create the application resource tag for resources created by this stack item.
• stack_item_label - Short form identifier for this stack. This value is used to create the Name resource tag for resources created by this stack item, and also serves as a unique key for re-use.

Virtual Private Cloud (VPC) parameters

• region - AWS region to be utilized.
• subnets - List of VPC subnets to associate with the auto scaling group.
• vpc_id - ID of the target VPC.

Launch template parameters

• ami - Amazon Machine Image (AMI) to associate with the launch template.
• associate_public_ip_address - (Optional) Flag for associating public IP addresses with instances managed by the auto scaling group.
• ebs_optimized - (Default: false) Flag to enable Elastic Block Storage (EBS) optimization.
• enable_monitoring - (Optional) Flag to enable detailed monitoring.
• instance_based_naming_enabled - (Optional) Flag to enable dynamic name tags on instances. The default format is stack_item_label-instance-id. Requires the instance to have the AWS CLI installed and an instance profile applied with the ec2:CreateTags action granted for the given instance.
• instance_name_prefix - (Optional) String to replace stack_item_label when instance_based_naming_enabled is set to true.
• instance_profile - (Optional) IAM instance profile to associate with the launch template.
• instance_tags - (Optional) A map of key/value pairs to be applied as tags to each instance. Requires the instance to have the AWS CLI installed and an instance profile applied with the ec2:CreateTags action granted for the given instance.
• instance_type - EC2 instance type to associate with the launch template.
• key_name - (Optional) SSH key pair to associate with the launch template.
• placement_tenancy - (Default: default) The tenancy of the instance. Valid values are default or dedicated.
• security_groups - (Optional) A list of associated security group IDs.
• spot_price - (Optional) The price to use for reserving spot instances.
• user_data - (Optional) Instance initialization data to associate with the launch template.

Block volume configuration

NOTES: Ephemeral block device support to be implemented in a future version. Module currently only offers support for a single additional volume in addition to root. All volume parameters are optional to the overall configuration, but those not marked optional here are required when specifying a volume.

• ebs_vol_del_on_term - (Default: true) Whether the volume should be destroyed on instance termination.
• ebs_vol_device_name - The name of the device to mount.
• ebs_vol_encrypted - (Optional) Whether the volume should be encrypted or not. Value is ignored when ebs_vol_snapshot_id has been specified.
• ebs_vol_iops - (Default: 2000) The amount of provisioned IOPS. Value is ignored for any volume type other than io1.
• ebs_vol_snapshot_id - (Optional) The Snapshot ID to mount.
• ebs_vol_size - (Optional) The size of the volume in gigabytes.
• ebs_vol_type - (Default: gp2) The type of volume. Valid values are standard, gp2 or io1.
• root_vol_del_on_term - (Default: true) Whether the volume should be destroyed on instance termination.
• root_vol_iops - (Default: 2000) The amount of provisioned IOPS. Value is ignored for any volume type other than io1.
• root_vol_size - (Optional) The size of the volume in gigabytes.
• root_vol_type - (Default: gp2) The type of volume. Valid values are standard, gp2 or io1.

Auto scaling group parameters

• default_cooldown - (Optional) The amount of time, in seconds, after a scaling activity completes before another scaling activity can start.
• desired_capacity - (Optional) The number of Amazon EC2 instances that should be running in the group.
• enabled_metrics - (Optional) A list of metrics to collect. The allowed values are 'GroupMinSize', 'GroupMaxSize', 'GroupDesiredCapacity', 'GroupInServiceInstances', 'GroupPendingInstances', 'GroupStandbyInstances', 'GroupTerminatingInstances', 'GroupTotalInstances'.
• force_delete - (Default: false) Flag to allow deletion of the auto scaling group without waiting for all instances in the pool to terminate.
• hc_check_type - (Optional) Type of health check performed by the auto scaling group. Valid values are ELB or EC2. Automatically set to EC2 when min_elb_capacity and wait_for_elb_capacity are unset and ELB when they are.
• hc_grace_period - (Optional) Time allowed after an instance comes into service before checking health.
• load_balancers - (Optional) List of load balancer names to associate with the auto scaling group.
• max_size - Maximum number of instances allowed by the auto scaling group.
• min_elb_capacity - (Optional) Minimum number of healthy instances attached to the ELB that must be maintained during updates.
• min_size - Minimum number of instance to be maintained by the auto scaling group.
• placement_group - (Optional) The name of the placement group into which you'll launch your instances, if any.
• protect_from_scale_in - (Optional) Allows setting instance protection. The auto scaling group will not select instances with this setting for terminination during scale in events.
• suspended_processes - (Optional) A list of processes to suspend for the auto scaling group. The allowed values are 'Launch', 'Terminate', 'HealthCheck', 'ReplaceUnhealthy', 'AZRebalance', 'AlarmNotification', 'ScheduledActions', 'AddToLoadBalancer'. Note that if you suspend either the 'Launch' or 'Terminate' process types, it can prevent your auto scaling group from functioning properly.
• termination_policies - (Optional) A list of policies to decide how the instances in the auto scale group should be terminated. The allowed values are 'OldestInstance', 'NewestInstance', 'OldestLaunchTemplate', 'ClosestToNextInstanceHour', 'Default'.
• wait_for_capacity_timeout - (Default: 10m) A maximum duration that Terraform should wait for ASG managed instances to become healthy before timing out.
• wait_for_elb_capacity - 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.)

Usage

NOTE: These examples assume that valid AWS credentials have been provided as environment variables.

Common

provider "aws" {
  region = "us-east-1"
}

data "template_file" "user_data" {
  template = "${file("../templates/user_data.tpl")}"
}

Basic ASG

module "asg" {
  source = "github.com/unifio/terraform-aws-asg//group"

  # Resource tags
  stack_item_fullname = "Application stack"
  stack_item_label    = "app-prod"

  # VPC parameters
  region  = "us-east-1"
  subnets = "subnet-3315e85a,subnet-3bbaaf43,subnet-ec1326a6"
  vpc_id  = "vpc-0f986c66"

  # LT parameters
  ami                           = "ami-0b33d91d"
  enable_monitoring             = true
  instance_based_naming_enabled = true
  instance_type                 = "m4.large"
  key_name                      = "ops"
  security_groups               = "sg-c1afc0a8,sg-7e33f32f"
  spot price                    = "0.010"
  user_data                     = "${template_file.user_data.rendered}"

  # ASG parameters
  max_size = 2
  min_size = 2
}

ASG w/ ELB

resource "aws_elb" "elb" {
.
.
}

resource "aws_iam_instance_profile" "terraform" {
.
.
}

module "asg" {
  source = "github.com/unifio/terraform-aws-asg//group"

  # Resource tags
  stack_item_fullname = "Application stack"
  stack_item_label    = "app-prod"

  # VPC parameters
  region  = "us-east-1"
  subnets = "subnet-3315e85a,subnet-3bbaaf43,subnet-ec1326a6"
  vpc_id  = "vpc-0f986c66"

  # LT parameters
  ami                           = "ami-0b33d91d"
  ebs_vol_device_name           = "/dev/xvdb"
  ebs_vol_encrypted             = true
  ebs_vol_size                  = 2
  ebs_vol_snapshot_id           = "snap-62d9d283"
  enable_monitoring             = true
  instance_based_naming_enabled = true
  instance_name_prefix          = "supercool"
  instance_tags                 = "${map("env","production")}"
  instance_type                 = "t2.medium"
  instance_profile              = "${aws_iam_instance_profile.terraform.id}"
  key_name                      = "ops"
  user_data                     = "${template_file.user_data.rendered}"

  # ASG parameters
  desired_capacity = 2
  load_balancers   = "${aws_elb.elb.id}"
  max_size         = 3
  min_elb_capacity = 2
  min_size         = 1
}

Outputs

• asg_id - ID of the auto scaling group
• asg_name - Name of the auto scaling group
• lt_id - ID of the launch template
• sg_id - ID of the security group

Policy Module

The policy module will provision auto scaling policy, auto scaling notification, CloudWatch monitor and SNS topic resources. Both absolute and percentage based simple scaling schemes are supported.

Input Variables

Resource labels

• stack_item_fullname - Long form descriptive name for this stack item. This value is used to create the application resource tag for resources created by this stack item.
• stack_item_label - Short form identifier for this stack. This value is used to create the Name resource tag for resources created by this stack item, and also serves as a unique key for re-use.

Auto scaling group parameters

• asg_name - Name of the ASG to associate the alarm with.

Notification parameters

• notifications - List of events to associate with the auto scaling notification.
  • Defaults (Comma separated String):
    • autoscaling:EC2_INSTANCE_LAUNCH
    • autoscaling:EC2_INSTANCE_TERMINATE
    • autoscaling:EC2_INSTANCE_LAUNCH_ERROR
    • autoscaling:EC2_INSTANCE_TERMINATE_ERROR

Policy parameters

• adjustment_type - Specifies the scaling adjustment. Valid values are ChangeInCapacity, ExactCapacity and PercentChangeInCapacity.
• cooldown - Seconds between auto scaling activities.
• scaling_adjustment - The number of instances involved in a scaling action.

Monitor parameters

• comparison_operator - Arithmetic operation to use when comparing the thresholds. Valid values are GreaterThanOrEqualToThreshold, GreaterThanThreshold, LessThanThreshold and LessThanOrEqualToThreshold.
• evaluation_periods - The number of periods over which data is compared to the specified threshold.
• metric_name - Name for the alarm's associated metric.
• name_space - (Default: AWS/EC2) The namespace for the alarm's associated metric.
• period - The period in seconds over which the specified statistic is applied.
• statistic - (Default: Average) The statistic to apply to the alarm's associated metric. Valid values are SampleCount, Average, Sum, Minimum and Maximum.
• threshold - The value against which the specified statistic is compared.
• treat_missing_data - (Default: missing) How alarms handle missing data points. Valid values are:
  • missing - Missing (the alarm looks back farther in time to find additional data points)
  • ignore - Good ("Not Breaching," treated as a data point that is within the threshold)
  • breaching - Bad ("Breaching," treated as a data point that is breaching the threshold)
  • notBreaching - Ignored (the current alarm state is maintained)

Usage

NOTE: These examples assume that valid AWS credentials have been provided as environment variables.

Common

provider "aws" {
  region = "us-east-1"
}

Absolute policy

module "absolute_policy" {
  source = "github.com/unifio/terraform-aws-asg//policy"

  # Resource tags
  stack_item_fullname = "Application stack"
  stack_item_label    = "app-prod"

  # ASG parameters
  asg_name = "example_asg"

  # Monitor parameters
  adjustment_type     = "ExactCapacity"
  comparison_operator = "LessThanOrEqualToThreshold"
  cooldown            = 300
  evaluation_periods  = 2
  metric_name         = "CPUUtilization"
  period              = 120
  scaling_adjustment  = 4
  threshold           = 10
  treat_missing_data  = "breaching"
}

Percentage policy

module "percentage_policy" {
  source = "github.com/unifio/terraform-aws-asg//policy"

  # Resource tags
  stack_item_fullname      = "application"
  stack_item_label         = "ops"

  # ASG parameters
  asg_name = "example_asg"

  # Monitor parameters
  adjustment_type          = "PercentChangeInCapacity"
  comparison_operator      = "GreaterThanOrEqualToThreshold"
  cooldown                 = 300
  evaluation_periods       = 2
  metric_name              = "CPUUtilization"
  period                   = 120
  scaling_adjustment       = 4
  threshold                = 10
  treat_missing_data       = "breaching"
}

Outputs

• sns_arn - Resource name of the Simple Notification Service (SNS) topic.

Examples

See the examples directory for a complete set of example source files.

License

MPL 2.0. See LICENSE for full details.