When writing complex templates you are encouraged to break up your template into separate smaller templates. These can then be brought together using template resources. This is a mechanism to define a resource using a template, thus composing one logical stack with multiple templates. Template resources provide a feature similar to the AWS::CloudFormation::Stack resource, but also provide a way to: Define new resource types and build your own resource library. Override the default behaviour of existing resource types. To achieve this: The Orchestration client gets the associated template files and passes them along in the files section of the POST stacks/ API request. The environment in the Orchestration engine manages the mapping of resource type to template creation. The Orchestration engine translates template parameters into resource properties. The following examples illustrate how you can use a custom template to define new types of resources. These examples use a custom template stored in a my_nova.yml file: heat_template_version: 2013-05-23 parameters: key_name: type: string description: Name of a KeyPair resources: server: type: OS::Nova::Server properties: key_name: {get_param: key_name} flavor: m1.small image: ubuntu-trusty-x86_64

The following template defines the my_nova.yaml file as value for the type property of a resource: heat_template_version: 2013-05-23 resources: my_server: type: my_nova.yaml properties: key_name: my_key The key_name argument of the my_nova.yaml template gets its value from the key_name property of the new template. The above reference to my_nova.yaml assumes it is in the same directory. You can use any of the following forms: Relative path (my_nova.yaml) Absolute path (file:///home/user/templates/my_nova.yaml) Http URL (http://example.com/templates/my_nova.yaml) Https URL (https://example.com/templates/my_nova.yaml) To create the stack run: $ heat stack-create -f main.yaml stack1

You can associate a name to the my_noya.yaml template in an environment file. If the name is already known by the Orchestration module then your new resource will override the default one. In the following example a new OS::Nova::Server resource overrides the default resource of the same name. An env.yaml environment file holds the definition of the new resource: resource_registry: "OS::Nova::Server": my_nova.yaml See for more detail about environment files. You can now use the new OS::Nova::Server in your new template: resources: my_server: type: OS::Nova::Server properties: key_name: my_key To create the stack run: $ heat stack-create -f main.yaml -e env.yaml example-two