Feature request: Allow aws_instance resource to create and manage spot instances

[tomelliff]

I haven't taken a particularly long look at the code to see how much impact this would have but it would be nice if the aws_instance resource could be used to manage spot instances instead of having to explicitly use the aws_spot_instance_request resource.

This would simplify being able to switch between spot and on demand requests without duplicating code. As it is I have a module that creates EC2 instances and then a bunch of other dependent resources (Route53 records, Cloudwatch alarms etc) and I'm going to have to duplicate the aws_instance resource plus all the resources dependent on it to use the aws_spot_instance_request and also make them conditional on whether a spot price has been set.

So as a minimal example I'll have something like:

variable "instance_count" {
  default = 1
}

variable "spot_price" {
  default = ""
}

data "aws_ami" "ubuntu" {
  most_recent = true

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-trusty-14.04-amd64-server-*"]
  }

  filter {
    name   = "virtualization-type"
    values = ["hvm"]
  }

  owners = ["099720109477"] # Canonical
}

resource "aws_instance" "instance" {
  count         = "${var.spot_price == "" ? var.instance_count : 0}"
  ami           = "${data.aws_ami.ubuntu.id}"
  instance_type = "t2.micro"

  tags {
    Name = "${var.name}${var.instance_count > 1 ? format("-%v", count.index+1) : ""}.${var.domain}"
  }
}

resource "aws_spot_instance_request" "instance" {
  count         = "${var.spot_price != "" ? var.instance_count : 0}"
  ami           = "${data.aws_ami.ubuntu.id}"
  instance_type = "t2.micro"
  spot_price    = "${var.spot_price}"

  tags {
    Name = "${var.name}${var.instance_count > 1 ? format("-%v", count.index+1) : ""}.${var.domain}"
  }
}

data "aws_vpc" "vpc" {
  tags {
    Name = "myvpc"
  }
}

data "aws_route53_zone" "zone" {
  name   = "example.com"
  vpc_id = "${data.aws_vpc.selected.id}"
}

resource "aws_route53_record" "on_demand_record" {
  count   = "${var.spot_price == "" ? var.instance_count : 0}"
  zone_id = "${data.aws_route53_zone.zone.zone_id}"
  name    = "${var.name}${var.instance_count > 1 ? format("-%v", count.index+1) : ""}.example.com"
  type    = "A"
  ttl     = "60"

  records = ["${element(aws_instance.instance.*.private_ip, count.index)}"]
}

resource "aws_route53_record" "spot_record" {
  count   = "${var.spot_price != "" ? var.instance_count : 0}"
  zone_id = "${data.aws_route53_zone.zone.zone_id}"
  name    = "${var.name}${var.instance_count > 1 ? format("-%v", count.index+1) : ""}.example.com"
  type    = "A"
  ttl     = "60"

  records = ["${element(aws_spot_instance_request.instance.*.private_ip, count.index)}"]
}

But with a lot more duplicated configuration between the aws_instance and aws_spot_instance_request and also anything else that needs the instance id, private IP address or other computed attributes.

Instead I'd love to just do:

variable "instance_count" {
  default = 1
}

variable "spot_price" {
  default = ""
}

data "aws_ami" "ubuntu" {
  most_recent = true

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-trusty-14.04-amd64-server-*"]
  }

  filter {
    name   = "virtualization-type"
    values = ["hvm"]
  }

  owners = ["099720109477"] # Canonical
}

resource "aws_instance" "instance" {
  count         = "${var.instance_count}"
  ami           = "${data.aws_ami.ubuntu.id}"
  instance_type = "t2.micro"
  spot_price    = "${var.spot_price}"

  tags {
    Name = "${var.name}${var.instance_count > 1 ? format("-%v", count.index+1) : ""}.${var.domain}"
  }
}

data "aws_vpc" "vpc" {
  tags {
    Name = "myvpc"
  }
}

data "aws_route53_zone" "zone" {
  name   = "example.com"
  vpc_id = "${data.aws_vpc.selected.id}"
}

resource "aws_route53_record" "record" {
  count   = "${var.instance_count}"
  zone_id = "${data.aws_route53_zone.zone.zone_id}"
  name    = "${var.name}${var.instance_count > 1 ? format("-%v", count.index+1) : ""}.example.com"
  type    = "A"
  ttl     = "60"

  records = ["${element(aws_instance.instance.*.private_ip, count.index)}"]
}

Where the aws_instance resource takes an optional spot_price (plus other spot related config) and if it gets an empty string or isn't provided then it creates an on demand instance instead.

Would people be open to complicating the code in the aws_instance module to allow for this simpler interface? I'd guess it probably adds a fair bit more complexity to things in the code but I'm not sure if there's an specific steer away from that if it enables users (the vast majority of people) to more easily do something like this.

[tomelliff]

Sounds like this should be much easier with this announcement today: https://aws.amazon.com/blogs/aws/amazon-ec2-update-streamlined-access-to-spot-capacity-smooth-price-changes-instance-hibernation/

Looks like the API docs/SDK haven't been updated just yet but checking the diffs on the SDK (https://github.com/aws/aws-sdk-go/pull/1666/files#diff-68798fbeff74277f6e5c5ab6f1cf92c6) it looks like things have been reworked a lot to expose a new LaunchTemplate structure.

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