According to my cloudwatch logs, my lambda functions never fire on the initial launch of my autoscaling group. The only time I have ever seen the eventbridge send an event to my lambda function is when i increased the desired capacity from 0 to 1. Whenever my desired capacity starts at 1 I get absolutely nothing. My goal ultimately is to assign an elastic ip address to all my autoscaled instances. I’m trying to use a lambda function to accomplish this, however its proving to not be simple.

Has anyone ever had a similar problem to this?

resource "aws_autoscaling_group" "ssh_proxy_group" {
  launch_template {
    id      = xxx
    version = "$Latest"
  }

  desired_capacity    = 0
  min_size            = 0
  max_size            = 20
}

resource "aws_autoscaling_policy" "scale_out_policy" {
  name                   = "ScaleOutPolicy"
  scaling_adjustment     = 1  # Number of instances to add
  adjustment_type        = "ChangeInCapacity"
  cooldown               = 300  # Time between scaling activities (5 minutes)
  autoscaling_group_name = aws_autoscaling_group.ssh_proxy_group.name
}

resource "aws_cloudwatch_event_rule" "instance_launch_rule" {
  name        = "instance-launch-rule"
  description = "Triggers when an EC2 instance is successfully launched by the Auto Scaling group."

  event_pattern = jsonencode({
    source = ["aws.autoscaling"],
    "detail-type" = ["EC2 Instance Launch Successful"],
    detail = {
      AutoScalingGroupName = [aws_autoscaling_group.ssh_proxy_group.name]
    }
  })
}

resource "aws_lambda_permission" "allow_eventbridge" {
  statement_id  = "AllowExecutionFromEventBridge"
  action        = "lambda:InvokeFunction"
  function_name = aws_lambda_function.allocate_ip_to_ec2.function_name
  principal     = "events.amazonaws.com"
  source_arn    = aws_cloudwatch_event_rule.instance_launch_rule.arn
}

resource "aws_cloudwatch_event_target" "trigger_lambda" {
  rule = aws_cloudwatch_event_rule.instance_launch_rule.name
  arn  = aws_lambda_function.allocate_ip_to_ec2.arn

  depends_on = [aws_lambda_permission.allow_eventbridge]
}