Getting Started¶

This guide walks you through deploying the update-dns module for your Auto Scaling Group.

Prerequisites¶

AWS Resources¶

Before deploying, you need:

A Route53 hosted zone -- the zone where DNS records will be created
An Auto Scaling Group -- or a plan to create one (the ASG name must be known before deploying this module)

Terraform Version¶

Terraform >= 1.5
AWS provider >= 5.11, < 7.0

Step-by-Step Deployment¶

Step 1: Define the ASG Name¶

The ASG name must be known before creating the module because it's used to set up the EventBridge rule. Use a local value:

locals {
  asg_name = "my-web-servers"
}

Step 2: Create the update-dns Module¶

module "update-dns" {
  source  = "registry.infrahouse.com/infrahouse/update-dns/aws"
  version = "1.3.0"

  asg_name        = local.asg_name
  route53_zone_id = data.aws_route53_zone.my_zone.zone_id
  alarm_emails    = ["ops-team@example.com"]
}

Step 3: Create the ASG with Initial Lifecycle Hook¶

The initial_lifecycle_hook ensures DNS records are created for the very first instances that launch with the ASG:

resource "aws_autoscaling_group" "web" {
  name                = local.asg_name
  min_size            = 1
  max_size            = 3
  vpc_zone_identifier = var.subnet_ids

  launch_template {
    id      = aws_launch_template.web.id
    version = "$Latest"
  }

  initial_lifecycle_hook {
    lifecycle_transition = "autoscaling:EC2_INSTANCE_LAUNCHING"
    name                 = module.update-dns.lifecycle_name_launching
  }

  depends_on = [module.update-dns]
}

Step 4: Create Lifecycle Hooks for Ongoing Events¶

These hooks handle DNS updates for instances that launch or terminate after the ASG is created:

resource "aws_autoscaling_lifecycle_hook" "launching" {
  autoscaling_group_name = aws_autoscaling_group.web.name
  lifecycle_transition   = "autoscaling:EC2_INSTANCE_LAUNCHING"
  name                   = module.update-dns.lifecycle_name_launching
  heartbeat_timeout      = 3600
}

resource "aws_autoscaling_lifecycle_hook" "terminating" {
  autoscaling_group_name = aws_autoscaling_group.web.name
  lifecycle_transition   = "autoscaling:EC2_INSTANCE_TERMINATING"
  name                   = module.update-dns.lifecycle_name_terminating
  heartbeat_timeout      = 3600
}

Step 5: Apply and Verify¶

terraform init
terraform plan
terraform apply

After applying, verify by checking the Route53 hosted zone for new A records corresponding to your ASG instances.

After the first deployment, you'll receive an email at the addresses specified in alarm_emails. Confirm the SNS subscription to start receiving Lambda monitoring alerts.