AWS Auto Scaling Group with Application Load Balancer using Terraform

aws-alb-asg.tf

# Create a basic ALB 
resource "aws_alb" "my-app-alb" {
  name = "my-app-alb"
}

# Create target groups with one health check per group
resource "aws_alb_target_group" "target-group-1" {
  name = "target-group-1"
  port = 80
  protocol = "HTTP"

  lifecycle { create_before_destroy=true }

  health_check {
    path = "/api/1/resolve/default?path=/service/my-service"
    port = 2001
    healthy_threshold = 6
    unhealthy_threshold = 2
    timeout = 2
    interval = 5
    matcher = "200"
  }
}

resource "aws_alb_target_group" "target-group-2" {
  name = "target-group-2"
  port = 80
  protocol = "HTTP"

  lifecycle { create_before_destroy=true }

  health_check {
    path = "/api/2/resolve/default?path=/service/my-service"
    port = 2010
    healthy_threshold = 6
    unhealthy_threshold = 2
    timeout = 2
    interval = 5
    matcher = "200"
  }
}

# Create a Listener 
resource "aws_alb_listener" "my-alb-listener" {
  default_action {
    target_group_arn = "${aws_alb_target_group.target-group-1.arn}"
    type = "forward"
  }
  load_balancer_arn = "${aws_alb.my-app-alb.arn}"
  port = 80
  protocol = "HTTP"
}

# Create Listener Rules
resource "aws_alb_listener_rule" "rule-1" {
  action {
    target_group_arn = "${aws_alb_target_group.target-group-1.arn}"
    type = "forward"
  }

  condition { field="path-pattern" values=["/api/1/resolve/default"] }

  listener_arn = "${aws_alb_listener.my-alb-listener.id}"
  priority = 100
}

resource "aws_alb_listener_rule" "rule-2" {
  action {
    target_group_arn = "${aws_alb_target_group.target-group-2.arn}"
    type = "forward"
  }

  condition { field="path-pattern" values=["/api/2/resolve/default"] }

  listener_arn = "${aws_alb_listener.my-alb-listener.id}"
  priority = 101
}

# Create an ASG that ties all of this together
resource "aws_autoscaling_group" "my-alb-asg" {
  name = "my-alb-asg"
  min_size = "3"
  max_size = "6"
  launch_configuration = "${aws_launch_configuration.my-app-alb.name}"
  termination_policies = [
    "OldestInstance",
    "OldestLaunchConfiguration",
  ]
  
  health_check_type = "ELB"

  depends_on = [
    "aws_alb.my-app-alb",
  ]

  target_group_arns = [
    "${aws_alb_target_group.target-group-1.arn}",
    "${aws_alb_target_group.target-group-2.arn}",
  ]

  lifecycle {
    create_before_destroy = true
  }
}