Allow spot instances to be used (#36)

* Allow spot instances to be used

An optional variable `spot_bid_price` has been added, which will allow
spot instances to be used for the ECS cluster.  When not specified (the
default), standard on-demand instances will still be used.

* Formatted files

.gitignore

@@ -0,0 +1,2 @@
+*.iml
+.idea/

README.md

@@ -46,7 +46,7 @@ extra_tags = [
 - `allowed_cidr_blocks` - List of subnets to allow into the ECS Security Group. Defaults to `["0.0.0.0/0"]`.
 - `ami` - A specific AMI image to use, eg `ami-95f8d2f3`. Defaults to the latest ECS optimized Amazon Linux AMI.
 - `ami_version` - Specific version of the Amazon ECS AMI to use (e.g. `2016.09`). Defaults to `*`. Ignored if `ami` is specified.
-- `heartbeat_timeout` - Heartbeat Timeout setting for how long it takes for the graceful shutodwn hook takes to timeout. This is useful when deploying clustered applications like consul that benifit from having a deploy between autoscaling create/destroy actions. Defaults to 180"
+- `heartbeat_timeout` - Heartbeat Timeout setting for how long it takes for the graceful shutdown hook takes to timeout. This is useful when deploying clustered applications like consul that benifit from having a deploy between autoscaling create/destroy actions. Defaults to 180"
 - `security_group_ids` - a list of security group IDs to apply to the launch configuration
 - `user_data` - The instance user data (e.g. a `cloud-init` config) to use in the `aws_launch_configuration`
 -  custom_iam_policy -  JSON containing the custom IAM policy for ECS nodes. Will overwrite the default one if set.
@@ -56,6 +56,8 @@ extra_tags = [
 - `consul_memory_reservation` - The soft limit (in MiB) of memory to reserve for the container, defaults 20
 - `registrator_memory_reservation` - The soft limit (in MiB) of memory to reserve for the container, defaults 20
 - `enable_agents` - Enable Consul Agent and Registrator tasks on each ECS Instance. Defaults to false
+- `spot_bid_price` - Use spot instances and request this bid price.  Note that with this option you risk your instances
+                     shutting down if the market price rises above your bid price. 
 
 Usage
 -----

main.tf

@@ -36,6 +36,7 @@ resource "aws_launch_configuration" "ecs" {
   iam_instance_profile        = "${aws_iam_instance_profile.ecs_profile.name}"
   security_groups             = ["${concat(list(aws_security_group.ecs.id), var.security_group_ids)}"]
   associate_public_ip_address = "${var.associate_public_ip_address}"
+  spot_price                  = "${var.spot_bid_price}"
 
   ebs_block_device {
     device_name           = "${var.ebs_block_device}"

variables.tf

@@ -56,6 +56,7 @@ variable "ebs_block_device" {
 }
 
 variable "extra_tags" {
+  type    = "list"
   default = []
 }
 
@@ -127,6 +128,11 @@ variable "servers" {
   description = "The number of servers to launch."
 }
 
+variable "spot_bid_price" {
+  default     = ""
+  description = "If specified, spot instances will be requested at this bid price.  If not specified, on-demand instances will be used."
+}
+
 variable "subnet_id" {
   type        = "list"
   description = "The AWS Subnet ID in which you want to delpoy your instances"