Infuse more flexibility into OpenStack Heat templates

OpenStack Heat example with environment files

To work with parameters in a more flexible way, admins can use OpenStack Heat environment files. Then, the HOT is processed by the heat command together with the environment file. In the template itself, admins set variables to refer to specific parameters and can define these parameters in the HOT itself -- which is the case in the example in Listing 1 below -- or in an environment file.

In this example, you can see the variable is referred to by using the curly braces: { get_resource: volume }.

This refers to the volume parameter, which admins define later in the template file. The term resources refers to the specific OpenStack components -- such as compute instances and security groups -- admins want to deploy.

Listing 1: Sample HOT contents

heat_template_version: 2014-10-16

description: A simple server

resources:

  server:

    type: OS::Nova::Server

    properties:

      block_device_mapping:

        - device_name: vda

          delete_on_termination: true

          volume_id: { get_resource: volume }

      flavor: m1.nano

      networks:

        - network: internal001

      user_data_format: RAW

      user_data: |

        #!/bin/sh

        while [ 1 ]; do echo $((13**99)) 1>/dev/null 2>&1; done

  volume:

    type: OS::Cinder::Volume

    properties:

      image: 'Cirros 0.3.4'

      size: 1

When admins define and use additional parameters in environment files, they have more flexibility with OpenStack Heat, especially as it increases scalability. To deploy a private cloud stack with both the HOT and the environment file, run the heat command, as in heat stack-create -r -f my-template.yaml -e my-env.yaml my-stack. Here, the -f option refers to the HOT, and the -e option refers to the environment file.

Environment files are not the only option for increased flexibility; admins could also include specific parameters when they run the heat command with the -P key=value argument.