Create a Heat template
Overview
Heat consumes templates written in "Heat Orchestration Template" (HOT) format.
- Written with YAML syntax
- Fully documented in the HOT specification
Heat can also use templates in AWS CloudFormation template format.
Template Repos
Complete Example
tl;dr: Here you can find a complete working template for CERN Cloud infrastructure.
heat_template_version: 2013-05-23
description: Simple template to deploy a single compute instance
parameters:
instance_name:
type: string
description: VM Name
constraints:
- allowed_pattern: "[a-zA-Z0-9-]+"
resources:
heatinstance:
type: OS::Nova::Server
properties:
name: { get_param: instance_name }
key_name: my_key
image: "CC7 - x86_64 [2018-08-20]"
flavor: m2.medium
metadata: {"cern-waitdns": "false"}
Structure
Templates have three sections:
# This is required.
heat_template_version: 2013-05-23
parameters:
# parameters go here
resources:
# resources go here (this section is required)
outputs:
# outputs go here
Version
The heat_template_version value is required and states which format is used in the present template.
heat_template_version: rocky
Only certain values are valid, such as rocky, 2018-08-31, queens, 2018-03-02, etc.
For updated information about Heat template versions and more details, check the HOT specification
Parameters
We can replace hardcoded values with parameters:
parameters:
image:
type: string
default: "CC7 - x86_64 [2018-08-20]"
description: >
image name or id used to boot our nova servers
Parameters can have:
- Types (string, number, comma_delimited_list, json, or boolean)
- Descriptions
- Constraints ("must be less than", "must be one of the following values", etc)
- Hints and help for UI display
Details in the hot specification.
When creating a stack, parameters can be specified:
On the command line with --parameter:
openstack stack create -t my_stack.yaml --parameter image="CC7 - x86_64 [2018-08-20]" my_stack
On the command line using an environment file:
openstack stack create -t my_stack.yaml -e my_env.yaml my_stack
An environment file is a YAML file with a parameters section containing values for parameters declared in your template:
parameters:
image: "CC7 - x86_64 [2018-08-20]"
Resources
The resources section specifies what resources Heat should create:
resources:
my_resource_id:
type: a_resource_type
properties:
property1: ...
property2: ...
Resources can depend on other resources. Explicitly:
my_server:
type: "OS::Nova::Server"
depends_on: my_network
Resource Documentation
Online documentation includes list of available resource types. You should refer to that document whenever you need a new resource.
You can also query Heat for information about available resource types:
$ openstack orchestration resource type list
+------------------------------------------+
| resource_type |
+------------------------------------------+
[...]
| OS::Nova::FloatingIP |
| OS::Nova::FloatingIPAssociation |
| OS::Nova::KeyPair |
| OS::Nova::Server |
[...]
And for information about a specific type:
$ openstack orchestration resource type show OS::Nova::Server
HeatTemplateFormatVersion: '2012-12-12'
Outputs:
accessIPv4: {Description: The manually assigned alternative public IPv4 address
of the server., Value: '{"Fn::GetAtt": ["Server", "accessIPv4"]}'}
Parameters:
admin_pass: {Description: The administrator password for the server., Type: String}
Resources:
Server:
Properties:
admin_pass: {Ref: admin_pass}
Type: OS::Nova::Server
Outputs
Sometimes we want to extract information about a stack:
outputs:
server_ip:
description: fixed ip assigned to the server
value: { get_attr: [my_server, first_address] }
These can be retrieved via heat output-list and heat output-show commands (and via API).