Deploying the latest build of a template (machine) image with #Xen #Orchestrator

In my current role we are using Packer to build images on a Xen Orchestrator environment, use a CI/CD system to install that image into both a Xen Template and an AWS AMI, and then we use Terraform to use that image across our estate. The images we build with Packer have this stanza in it:

locals {
  timestamp = regex_replace(timestamp(), "[- TZ:]", "")
}
variable "artifact_name" {
  default = "SomeLinux-version.iso"
}
source "xenserver-iso" "this" {
  vm_name = "${var.artifact_name}-${local.timestamp}"
  # more config below
}

As a result, the built images include a timestamp.

When we use the AMI in Terraform, we can locate it with this code:

variable "ami_name" {
  default = "SomeLinux-version.iso-"
}

data "aws_ami" "this" {
  most_recent = true

  filter {
    name   = "name"
    values = [var.ami_name]
  }

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

  owners = [var.owner]
}

But, because Xen doesn’t track when a template is created, instead I needed to do something different. Enter get_xoa_template.sh.

This script is invoked from your terraform like this:

variable "template_name" {
  default     = "SomeLinux-version.iso-"
  description = "A regex, partial or full string to match in the template name"
}

variable "poolname" {
  default = "MyPool"
}

data "external" "get_xoa_template" {
  program = [
    "/bin/bash", "${path.module}/get_xoa_template.sh",
    "--template", var.template_name,
    "--pool", var.poolname
  ]
}

data "xenorchestra_pool" "pool" {
  name_label = var.poolname
}

data "xenorchestra_template" "template" {
  name_label = data.external.get_xoa_template.result.is
  pool_id    = data.xenorchestra_pool.pool.id
}

And that’s how you do it. Oh, and if you need to pin to a specific version? Change the template_name value from the partial or regex version to the full version, like this:

variable "template_name" {
  # This assumes your image was minted at midnight on 1970-01-01
  default     = "SomeLinux-version.iso-19700101000000"
}

Featured image is “Barcelos and Braga-18” by “Graeme Churchard” on Flickr and is released under a CC-BY license.