Local Traffic Management

Our regional AWS load balancers can provide Local Traffic Management (LTM) services. By adding a layer of abstraction between DNS and our instances, we can take advantage of a number of patterns for maintaining our backing services with little or no downtime.

Chapter 6, Ephemeral Environments - Sandboxes for Experiments, will go into detail about those architectures, but for now, we will add our latest instance to the load balancer, then update DNS (our GTM) to point to our load balancer (our LTM) in addition to the existing instances—see the following changes made to the instanceAZ1c.tf file:

# Create a new load balancer
resource "aws_elb" "cloudelb" {
  name = "cloudpatterns-elb"
  availability_zones = ["us-east-1c"]

  listener {
    instance_port = 80
    instance_protocol = "http"
    lb_port = 80
    lb_protocol = "http"
  }

  health_check {
    healthy_threshold = 2
    unhealthy_threshold = 2
    timeout = 3
    target = "HTTP:80/"
    interval = 30
  }

  instances = ["${aws_instance.cheap_worker1c.id}"]
  cross_zone_load_balancing = true
  idle_timeout = 400
  connection_draining = true
  connection_draining_timeout = 400
}

Remove the aws_route53_record.www resource configuration from the main.tf file. Then, we'll destroy the A record used in the environment by performing the following instruction in the terraform destroy target=aws_route53_record.www bash panel. Now we will need to add a different type of DNS record; we'll create a new file called ltm.tf:

# Global Traffic Management using DNS
resource "aws_route53_record" "wwwltm" {
  zone_id = "${aws_route53_zone.book.zone_id}"
  name = "www"
  type = "cname"
  ttl = "300"
  records = ["${aws_elb.cloudelb.dns_name}"]
}

Plan and apply your Terraform to get your new CNAME record:

You will notice that your WordPress is still responding. The canonical name record allows us to point one DNS record at another. Using this pointer, AWS can scale our load balancer (LTM) up and down without us worrying about the ever-changing IP addresses. We can do the same thing with our service instances.