expanded readme for clarity on the problem this solves

Author: brandonjbjelland

README.md

@@ -1,9 +1,12 @@
 # terraform-aws-ebs-optimized
 
-A terraform module to return true (1) or false (0) based on if an instance type
-supports the EBS optmized flag. If you want to use different instance types and
-would rather use EBS optimization whenever possible, this module does the heavy
-lifting of determining if that's possible.
+A terraform module to return true or false based on if an instance type
+supports the EBS optmized flag. If you want to use various instance types and
+EBS optimization, this module does the heavy lifting of determining if that's
+possible. Without the module, EC2 instance creation would fail on unsupported
+types and -- even worse -- launch configurations will create normally but fail
+silently when instances attempt to launch. This module means you don't need to
+think about that problem.
 
 ## Usage example
 

examples/ebs_optimized_test_fixture/main.tf

@@ -26,18 +26,33 @@ data "aws_ami" "ubuntu" {
   owners = ["099720109477"] # Canonical
 }
 
+resource "aws_launch_configuration" "ebs_optimized" {
+  name_prefix   = "test_ebs_optimized"
+  image_id      = "${data.aws_ami.ubuntu.id}"
+  instance_type = "${var.supported_type}"
+  ebs_optimized = "${module.supported_ebs.answer}"
+}
+
+resource "aws_launch_configuration" "ebs_not_optimized" {
+  name_prefix   = "test_ebs_not_optimized"
+  image_id      = "${data.aws_ami.ubuntu.id}"
+  instance_type = "${var.unsupported_type}"
+
+  ebs_optimized = "${module.unsupported_ebs.answer}"
+}
+
 resource "aws_instance" "ebs_optimized" {
   ami           = "${data.aws_ami.ubuntu.id}"
   instance_type = "${var.supported_type}"
-  tags          = "${merge(local.tags, map("Name", "test_ebs_optimized"))}"
   ebs_optimized = "${module.supported_ebs.answer}"
+  tags          = "${merge(local.tags, map("Name", "test_ebs_optimized"))}"
 }
 
 resource "aws_instance" "ebs_not_optimized" {
   ami           = "${data.aws_ami.ubuntu.id}"
   instance_type = "${var.unsupported_type}"
-  tags          = "${merge(local.tags, map("Name", "test_not_ebs_optimized"))}"
   ebs_optimized = "${module.unsupported_ebs.answer}"
+  tags          = "${merge(local.tags, map("Name", "test_not_ebs_optimized"))}"
 }
 
 module "supported_ebs" {

main.tf

@@ -1,10 +1,13 @@
 /**
 # terraform-aws-ebs-optimized
 
-* A terraform module to return true (1) or false (0) based on if an instance type 
-* supports the EBS optmized flag. If you want to use different instance types and
-* would rather use EBS optimization whenever possible, this module does the heavy
-* lifting of determining if that's possible.
+* A terraform module to return true or false based on if an instance type
+* supports the EBS optmized flag. If you want to use various instance types and
+* EBS optimization, this module does the heavy lifting of determining if that's
+* possible. Without the module, EC2 instance creation would fail on unsupported
+* types and -- even worse -- launch configurations will create normally but fail
+* silently when instances attempt to launch. This module means you don't need to
+* think about that problem.
 
 * ## Usage example
 
@@ -15,12 +18,12 @@
 *   description = "Size/type of the host."
 *   default     = "m1.large"
 * }
-* 
+*
 * module "ebs_optimized" {
 *   source        = "terraform-aws-modules/ebs-optimized/aws"
 *   instance_type = "${var.web_type}"
 * }
-* 
+*
 * resource "aws_instance" "web" {
 *   ami           = "${data.aws_ami.ubuntu.id}"
 *   instance_type = "${var.web_type}"