A Terraform module for creating an Auto-Scaling Group and a launch configuration for it, for use with an Elastic Load Balancer. This module makes the following assumptions:

• You have subnets in a VPC and that you want your instances in two subnets (in two AZs)
• You can fully bootstrap your instances using an AMI + user_data
• You want to associate the ASG with an ELB
• Your instances behind the ELB will be in a VPC
• Your using a single Security Group for all instances in the ASG

• lc_name - The launch configuration name
• ami_id
• instance_type
• iam_instance_profile - The ARN of the Instance Profile the LC should launch instances with. E.g. arn:aws:iam::XXXXXXXXXXXX:instance-profile/my-instance-profile
• key_name - The SSH key name (uploaded to EC2) instances should be populated with.
• security_group - The Security Group ID that instances in the ASG
  • This is usually set to resolve to a security group you make in the same template as this module, e.g. "${module.sg_web.security_group_id_web}"
  • It needs to be customized based on the name of your module resource. should use.
• user_data - The path to the user_data file for the Launch Configuration.
  • Terraform will include the contents of this file in the Launch Configuration.
• asg_name - The Auto-Scaling group name.
• asg_number_of_instances - The number of instances we want in the ASG
  • This is used to populate the following ASG settings.
  • max_size
  • desired_capacity
• asg_minimum_number_of_instances - The minimum number of instances the ASG should maintain.
  • This is used for min_size
  • It defaults to 1
  • You can set it to 0 if you want the ASG to do nothing when an instances fails
• health_check_grace_period - Number of seconds for the health check time out. Defaults to 300.
• health_check_type - The health check type. Options are ELB and EC2. It defaults to ELB in this module.
• load_balancer_names - The name(s) of the ELB(s) to associate with the ASG, for settings it's backend instances. Ideally this is a reference to an ELB you're making in the same template as this ASG. Can be a CSV of ELB names if more than one is desired.
• availability_zones - CSV of availability zones (AZs) for the ASG. ex. "us-east-1a,us-east-1c"
• vpc_zone_subnets - CSV of VPC subnets to associate with ASG. There should be one subnet for each of the availability_zones. ex. "subnet-d2gd22,subnet-2kjn8qq"

• launch_config_id
• asg_id

You can use these in your terraform template with the following steps.

1.) Adding a module resource to your template, e.g. main.tf

module "my_autoscaling_group" {
  source = "github.com/terraform-community-modules/tf_aws_asg_elb"
  lc_name = "${var.lc_name}"
  ami_id = "${var.ami_id}"
  instance_type = "${var.instance_type}"
  iam_instance_profile = "${var.iam_instance_profile}"
  key_name = "${var.key_name}"

  //Using a reference to an SG we create in the same template.
  // - It needs to be customized based on the name of your module resource
  // - It is recommended that you use https://github.com/terraform-community-modules/tf_aws_sg/tree/master/sg_https_only
  //   for the SG
  security_group = "${module.sg_https_only.security_group_id_web}"

  user_data = "${var.user_data}"
  asg_name = "${var.asg_name}"
  asg_number_of_instances = "${var.asg_number_of_instances}"
  asg_minimum_number_of_instances = "${var.asg_minimum_number_of_instances}"

  //Using a reference to an SG we create in the same template
  load_balancer_names = "${module.my_elb.elb_name}"

  // The health_check_type can be EC2 or ELB and defaults to ELB
  health_check_type = "${var.health_check_type}"

  availability_zones = "${var.availability_zones}"
  vpc_zone_subnets = "${var.vpc_zone_subnets}"

  aws_access_key = "${var.aws_access_key}"
  aws_secret_key = "${var.aws_secret_key}"
  aws_region = "${var.aws_region}"
}

2.) Setting values for the following variables, either through terraform.tfvars or -var arguments on the CLI

• aws_access_key
• aws_secret_key
• aws_region
• lc_name
• ami_id
• instance_type
• iam_instance_profile
• key_name
• security_group
• user_data
• asg_name
• asg_number_of_instances.
• load_balancer_names
• availability_zones
• vpc_zone_subnets

Created and maintained by Brandon Burton (brandon@inatree.org).

Apache 2 Licensed. See LICENSE for full details.