Load balancing and simulating conditionals

If we were not using AWS in this book, or if we wanted to go the more complicated (but certainly more flexible) way, we would use our very own load balancer. But we won't, because we can simply take the Elastic Load Balancer (ELB) service of AWS and put application servers behind it.

This means we will add yet another resource to the application module. Add the following configuration right after the null_resource provisioners:

resource "aws_elb" "load-balancer" { 
  name = "application-load-balancer" 
  subnets = ["${var.subnets}"] 
  security_groups = "${aws_security_group.allow_http.id}"]  
 
  listener { 
    instance_port = 80 
    instance_protocol = "http" 
    lb_port = 80 
    lb_protocol = "http" 
  } 
 
  health_check { 
    healthy_threshold = 2 
    unhealthy_threshold = 2 
    timeout = 3 
    target = "TCP:80" 
    interval = 30 
  } 
 
  instances = ["${aws_instance.app-server.*.id}"] 
} 

This ELB is configured for the HTTP port, and...