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Step 20: Build multiple VMs with HEAT

Start

Previous steps outlined how to create a single VM. The next step is to create multiple VMs at the same time.

In this step, two VMs that share a common network will be created.

First Steps

To begin with, split the template into two parts. It is best practice to break larger setups up into multiple files.

First, start with a simple template which contains only the network and the port.

heat_template_version: 2014-10-16

description: A simple template which deploys 3 VMs

resources:

    ExampleNet:
        type: OS::Neutron::Net
        properties:
            name: ExampleNet

    ExampleSubnet:
        type: OS::Neutron::Subnet
        properties:
            name: ExampleSubnet
            dns_nameservers:
                - 8.8.8.8
                - 8.8.4.4
            network: {get_resource: ExampleNet}
            ip_version: 4
            cidr: 10.0.0.0/24
            allocation_pools:
            - {start: 10.0.0.10, end: 10.0.0.250}

This is the basic structure for your stack, the file can be saved under the name groups.yaml.

Create a new template exampleserver.yaml and define the VM here.

Make sure that name and network_id are not defined.

Use a valid value to fill image:. You can use the image name or ID. Exact image names / IDs can be obtained by running openstack image list. ß

heat_template_version: 2014-10-16

description: a single server description

parameters:
  network_id:
    type: string
  server_name:
    type: string

resources:
  VM:
    type: OS::Nova::Server
    properties:
      user_data_format: RAW
      image: Ubuntu 16.04 Xenial Xerus - Latest
      flavor: m1.small
      name: { get_param: server_name }
      networks:
        - port: { get_resource: ExamplePort }

  ExamplePort:
    type: OS::Neutron::Port
    properties:
      network: { get_param: network_id }

You can now modify your groups.yaml and add a resource group where you add the VMs with the required arguments. After the file has been updated, it can be saved as exampleserver.yaml

The next step is to integrate the second template created as a resource group. The number of instances, the names, etc. can also be specified here:

heat_template_version: 2014-10-16

description: A simple template which deploys 3 VMs

resources:
 
    ExampleVM:
        type: OS::Heat::ResourceGroup
        depends_on: ExampleSubnet
        properties:
            count: 3
            resource_def:
                type: exampleserver.yaml
                properties:
                    network_id: { get_resource: ExampleNet}
                    server_name: ExampleVM_%index%

    ExampleNet:
        type: OS::Neutron::Net
        properties:
            name: ExampleNet

    ExampleSubnet:
        type: OS::Neutron::Subnet
        properties:
            name: ExampleSubnet
            dns_nameservers:
                - 8.8.8.8
                - 8.8.4.4
            network: {get_resource: ExampleNet}
            ip_version: 4
            cidr: 10.0.0.0/24
            allocation_pools:
            - {start: 10.0.0.10, end: 10.0.0.250}

Now that you have supplied all data, you can create your stack:

openstack stack create -t groups.yaml <Name of the stack>

Conclusion

Congratulations, you went from creating a single VM with the web interface to creating full stacks with the OpenStack client. Several instances can now be rolled out at the same time using a template, a good starting point for OpenStack administration.