Initial input for HOT template guide and spec

This patch adds initial input for the HOT template guide and the HOT
specification.
Note that content so far is based on features implemented so far and
not forward-looking in any way. Whenever new features get implemented,
the guide and spec will be extended appropriately.

Contributes to blueprint hot-specification

Change-Id: I63d29ab0a1db6703b39f981161063d4fd9f97126
This commit is contained in:
Thomas Spatzier 2013-08-08 18:59:11 +02:00
parent f6b6cf8097
commit 514e9b746c
3 changed files with 668 additions and 1 deletions

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..
Licensed under the Apache License, Version 2.0 (the "License"); you may
not use this file except in compliance with the License. You may obtain
a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations
under the License.
=======================================
Heat Orchestration Template (HOT) Guide
=======================================
HOT is a new template format meant to replace the Heat CloudFormation-compatible
format (CFN) as the native format supported by the Heat over time.
This guide is targeted towards template authors and explains how to write
HOT templates based on examples. A detailed specification of HOT can be found
at :ref:`_hot_spec`.
------
Status
------
HOT support is still under development and needs more work to provide access to
all functionality currently available via the CFN compatible template interface.
This guide will be updated periodically whenever new features get implemented
for HOT.
----------------------------------
Writing a hello world HOT template
----------------------------------
This section gives an introduction on how to write HOT templates, starting from
very basic steps and then going into more and more detail by means of examples.
A most basic template
---------------------
The most basic template you can think of may contain only a single resource
definition using only predefined properties (along with the mandatory Heat
template version tag). For example, the template below could be used to simply
deploy a single compute instance.
::
heat_template_version: 2013-05-23
description: Simple template to deploy a single compute instance
resources:
my_instance:
type: OS::Nova::Compute
properties:
KeyName: my_key
ImageId: F18-x86_64-cfntools
InstanceType: m1.small
Each HOT template has to include the *heat_template_version* key with value
'2013-05-23' (the current version of HOT). While the *description* is optional,
it is good practice to include some useful text that describes what users can do
with the template. In case you want to provide a longer description that does
not fit on a single line, you can provide multi-line text in YAML, for example:
::
description: >
This is how you can provide a longer description
of your template that goes over several lines.
The *resources* section is required and must contain at least one resource
definition. In the example above, a compute instance is defined with fixed
values for the 'KeyName', 'ImageId' and 'InstanceType' parameters.
Note that all those elements, i.e. a key-pair with the given name, the image and
the flavor have to exist in the OpenStack environment where the template is
used. Typically a template is made more easily reusable, though, by defining a
set of *input parameters* instead of hard-coding such values.
Template input parameters
-------------------------
Input parameters defined in the *parameters* section of a HOT template (see also
:ref:`_hot_spec_parameters`) allow users to customize a template during
deployment. For example, this allows for providing custom key-pair names or
image IDs to be used for a deployment.
From a template author's perspective, this helps to make a template more easily
reusable by avoiding hardcoded assumptions.
Sticking to the example used above, it makes sense to allow users to provide
their custom key-pairs, provide their own image, and to select a flavor for the
compute instance. This can be achieved by extending the initial template as
follows:
::
heat_template_version: 2013-05-23
description: Simple template to deploy a single compute instance
parameters:
key_name:
type: string
description: Name of key-pair to be used for compute instance
image_id:
type: string
description: Image to be used for compute instance
instance_type:
type: string
description: Type of instance (flavor) to be used
resources:
my_instance:
type: OS::Nova::Compute
properties:
KeyName: { get_param: key_name }
ImageId: { get_param: image_id }
InstanceType: { get_param: instance_type }
In the example above, three input parameters have been defined that have to be
provided by the user upon deployment. The fixed values for the respective
resource properties have been replaced by references to the corresponding
input parameters by means of the *get_param* function (see also
:ref:`_hot_spec_intrinsic_functions`).
You can also define default values for input parameters which will be used in
case the user does not provide the respective parameter during deployment. For
example, the following definition for the *instance_type* parameter would select
the 'm1.small' flavor unless specified otherwise be the user.
::
parameters:
instance_type:
type: string
description: Type of instance (flavor) to be used
default: m1.small
Another option that can be specified for a parameter is to hide its value when
users request information about a stack deployed from a template. This is
achieved by the *hidden* attribute and useful, for example when requesting
passwords as user input:
::
parameters:
database_password:
type: string
description: Password to be used for database
hidden: true
Restricting user input
~~~~~~~~~~~~~~~~~~~~~~
In some cases you might want to restrict the values of input parameters that
users can supply. For example, you might know that the software running in a
compute instance needs a certain amount of resources so you might want to
restrict the *instance_type* parameter introduced above. Parameters in HOT
templates can be restricted by adding a *constraints* section (see also
:ref:`_hot_spec_parameters_constraints`).
For example, the following would allow only three values to be provided as input
for the *instance_type* parameter:
::
parameters:
instance_type:
type: string
description: Type of instance (flavor) to be used
constraints:
- allow_values: [ m1.medium, m1.large, m1.xlarge ]
description: Value must be one of m1.medium, m1.large or m1.xlarge.
The *constraints* section allows for defining a list of constraints that must
all be fulfilled by user input. For example, the following list of constraints
could be used to clearly specify format requirements on a password to be
provided by users:
::
parameters:
database_password:
type: string
description: Password to be used for database
hidden: true
constraints:
- length: { min: 6, max: 8 }
description: Password length must be between 6 and 8 characters.
- allowed_pattern: "[a-zA-Z0-9]+"
description: Password must consist of characters and numbers only.
- allowed_pattern: "[A-Z]+[a-zA-Z0-9]*"
description: Password must start with an uppercase character.
Note that you can define multiple constraints of the same type. Especially in
the case of allowed patterns this not only allows for keeping regular
expressions simple and maintainable, but also for keeping error messages to be
presented to users precise.
Providing template outputs
--------------------------
In addition to template customization through input parameters, you will
typically want to provide outputs to users, which can be done in the
*outputs* section of a template (see also :ref:`_hot_spec_outputs`).
For example, the IP address by which the instance defined in the example
above can be accessed should be provided to users. Otherwise, users would have
to look it up themselves. The definition for providing the IP address of the
compute instance as an output is shown in the following snippet:
::
outputs:
instance_ip:
description: The IP address of the deployed instance
value: { get_attr: [my_instance, PublicIp] }
Output values are typically resolved using intrinsic function such as
the *get_attr* function in the example above (see also
:ref:`_hot_spec_intrinsic_functions`).

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..
Licensed under the Apache License, Version 2.0 (the "License"); you may
not use this file except in compliance with the License. You may obtain
a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations
under the License.
.. _hot_spec:
===============================================
Heat Orchestration Template (HOT) Specification
===============================================
HOT is a new template format meant to replace the Heat CloudFormation-compatible
format (CFN) as the native format supported by the Heat over time.
This specification explains in detail all elements of the HOT template format.
An example driven guide to writing HOT templates can be found
at :ref:`_hot_guide`.
------
Status
------
HOT support is still under development and needs more work to provide access to
all functionality currently available via the CFN compatible template interface.
This specification will be updated periodically whenever new features get
implemented for HOT.
------------------
Template Structure
------------------
HOT templates are defined in YAML and follow the structure outlined below.
::
heat_template_version: 2013-05-23
description: # a description of the template
parameters:
# declaration of input parameters
resources:
# declaration of template resources
outputs:
# declaration of output parameters
heat_template_version
This key with value *2013-05-23* (or a later date) indicates that the YAML
document is a HOT template of the specified version.
description
This *optional* key allows for giving a description of the template, or the
workload that can be deployed using the template.
parameters
This section allows for specifying input parameters that have to be provided
when instantiating the template. The section is *optional* and can be
omitted when no input is required.
resources
This section contains the declaration of the single resources of the
template. This section is mandatory and at least one resource must be
defined in any HOT template.
outputs
This section allows for specifying output parameters available to users once
the template has been instantiated. This section is *optional* and can be
omitted when no output values are required.
.. _hot_spec_parameters:
------------------
Parameters Section
------------------
The *parameters* section allows for specifying input parameters that have to be
provided when instantiating the template. Such parameters are typically used to
customize each deployment (e.g. by setting custom user names or passwords) or
for binding to environment-specifics like certain images.
Each parameter is specified in a separated nested block with the name of the
parameters defined in the first line and additional attributes such as type or
default value defined as nested elements.
::
parameters:
<param name>:
type: <string | number | json | comma_delimited_list>
description: <description of the parameter>
default: <default value for parameter>
hidden: <true | false>
constraints:
<parameter constraints>
param name
The name of the parameter is defined at the top of each parameter block.
type
This attribute specifies the type of parameter. Currently supported types
are *string*, *number*, *comma_delimited_list* or *json*.
description
This *optional* attribute allows for giving a human readable description of
the parameter.
default
This *optional* attribute allows for defining a default value for the
parameters which will be used in case the parameter is not specified by the
user during deployment.
hidden
This *optional* attribute allows for specifying whether the parameters
should be hidden when showing information about a stack created from the
template at runtime (e.g. for hiding passwords that were specified as
parameters). If not specified, the default value 'false' will be used.
constraints
This *optional* block allows for specifying additional constraints on the
parameter, such as minimum or maximum values for numeric parameters.
The following example shows a minimalistic definition of two parameters. Note
that the description is actually optional, but is good practice to provide a
useful description for each parameter.
::
parameters:
user_name:
type: string
description: User name to be configured for the application
port_number:
type: number
description: Port number to be configured for the web server
.. _hot_spec_parameters_constraints:
Parameter Constraints
---------------------
The *constraints* block of a parameter definition allows for defining additional
validation constraints that apply to the value of the parameter. At
instantiation time of the template, user provided parameter values are validated
against those constraints to make sure the provided values match expectations of
the template author.
Constraints are defined in the form of a bulleted list according to the
following syntax:
::
constraints:
- <constraint type>: <constraint definition>
description: <constraint description>
constraint type
The constraint type specifies the kind of constraint defined in the current
bulleted list item. The set of currently supported constraints is given
below.
constraint definition
This value defines the actual constraint, depending on the constraint type.
The concrete syntax for each constraint type is given below.
description
This *optional* attribute allows for specifying a concrete description of
the current constraint. This text will be presented to the user, for
example, when the provided input value for a parameter violates the
constraint. If omitted, a default validation message will be presented to
the user.
The following example show the definition of a string parameter with two
constraints. Note that while the descriptions for each constraint are optional,
it is good practice to provide concrete descriptions so useful messages can be
presented to the user at deployment time.
::
parameters:
user_name:
type: string
description: User name to be configured for the application
constraints:
- length: { min: 6, max: 8 }
description: User name must be between 6 and 8 characters
- allowed_pattern: "[A-Z]+[a-zA-Z0-9]*"
description: User name must start with an uppercase character
The following sections list the supported types of parameter constraints, along
with the concrete syntax for each type.
length
~~~~~~
The *length* constraint applies to parameters of type *string* and allows for
defining a lower and upper limit for the length of the string value. The syntax
for the length constraint is:
::
length: { min: <lower limit>, max: <upper limit> }
It is possible to define a length constraint with only a lower limit or an
upper limit. However, at least one of *min* or *max* must be specified.
range
~~~~~
The *range* constraint applies to parameters of type *number* and allows for
defining a lower and upper limit for the numeric value of the parameter. The
syntax of the range constraint is:
::
range: { min: <lower limit>, max: <upper limit> }
It is possible to define a range constraint with only a lower limit or an
upper limit. However, at least one of *min* or *max* must be specified.
The minimum or maximum boundaries are included in the range. For example, the
following range constraint would allow for all numeric values between 0 and 10.
::
range: { min: 0, max: 10 }
allowed_values
~~~~~~~~~~~~~~
The *allowed_values* constraint applies to parameters of type string or number
and allows for specifying a set of possible values for a parameter. At
deployment time, the user provided value for the respective parameter must
match one of the elements of the specified list. The syntax of the
allowed_values constraint is:
::
allowed_values: [ <value>, <value>, ... ]
Alternatively, the YAML bulleted list notation can be used:
::
allowed_values:
- <value>
- <value>
- ...
For example:
::
parameters:
instance_type:
type: string
description: Instance type for compute instances
constraints:
allowed_values:
- m1.small
- m1.medium
- m1.large
allowed_pattern
~~~~~~~~~~~~~~~
The *allowed_pattern* constraint applies to parameters of type string and allows
for specifying a regular expression against which a user provided parameter
value must evaluate at deployment
The syntax of the allowed_pattern constraint is:
::
allowed_pattern: <regular expression>
For example:
::
parameters:
user_name:
type: string
description: User name to be configured for the application
constraints:
- allowed_pattern: "[A-Z]+[a-zA-Z0-9]*"
description: User name must start with an uppercase character
.. _hot_spec_resources:
-----------------
Resources Section
-----------------
In the *resources* section, the templates for actual resources that will make up
a stack deployed from the HOT template (e.g. compute instances, networks,
storage volumes) are defined.
Each resource is defined as a separate block in the resources section according
to the syntax below.
::
resources:
<resource ID>:
type: <resource type>
properties:
<property name>: <property value>
# more resource specific metadata
resource ID
A resource block is headed by the resource ID, which must be unique within
the resource section of a template.
type
This attribute specifies the type of resource, such as OS::Nova::Compute.
properties
This section contains a list of resource specific properties. The property
value can be provided in place, or can be provided via a function
(see :ref:`_hot_spec_intrinsic_functions`).
Depending on the type of resource, the resource block might include more
resource specific metadata. Basically all resource types that can be used in
CFN templates can also be used in HOT templates, adapted to the YAML structure
as outlined above.
Below is an example of a simple compute resource definition with some fixed
property values.
::
resources:
my_instance:
type: OS::Nova::Compute
properties:
instance_type: m1.small
image_id: F18-x86_64-cfntools
.. _hot_spec_outputs:
---------------
Outputs Section
---------------
In the *outputs* section, any output parameters that should be available to the
user can be defined. Typically, this would be, for example, parameters such as
IP addresses of deployed instances, or URLs of web applications deployed as part
of a stack.
Output parameters are defined according to the following syntax:
::
outputs:
<parameter name>: <parameter value>
parameter name
The name of the output parameter is defined as a key in the outputs section.
parameter value
This element specifies the value of the output parameter. Typically, this
will be resolved by means of a function, e.g. by getting an attribute value
of one of the stack's resources (see also
:ref:`_hot_spec_intrinsic_functions`).
The example below shows, how the public IP address of a compute resource can be
defined as an output parameter.
::
outputs:
instance_ip: { get_attr: [my_instance, PublicIp] }
.. _hot_spec_intrinsic_functions:
-------------------
Intrinsic Functions
-------------------
HOT provides a set of intrinsic functions that can be used inside HOT templates
to perform specific tasks, such as getting the value of a resource attribute at
runtime. A definition of all intrinsic functions available in HOT is given
below.
get_param
---------
The *get_param* function allows for referencing an input parameter of a template
from anywhere within a template. At runtime, it will be resolved to the value
provided for this input parameter. The syntax of the get_param function is as
follows:
::
get_param: <parameter name>
The *parameter name* of the input parameter to be resolved is given as single
parameter to this function. A sample use of this function in context of a
resource definition is shown below.
::
parameters:
instance_type:
type: string
description: Instance type to be used.
resources:
my_instance:
type: OS::Nova::Compute
properties:
instance_type: { get_param: instance_type}
get_attr
--------
The *get_attr* function allows for referencing an attribute of a resource. At
runtime, it will be resolved to the value of an attribute of a resource instance
created from the respective resource definition of the template.
The syntax of the get_attr function is as follows:
::
get_attr: [ <resource ID>: <attribute name> ]
resource ID
This parameter specifies the resource the attribute of which shall be
resolved. This resource must be defined within the *resources* section of
the template (see also :ref:`_hot_spec_resources`).
attribute name
This parameter specifies the attribute to be resolved.
An example of using the get_attr function is shown below:
::
resources:
my_instance:
type: OS::Nova::Compute
# ...
outputs:
instance_ip: { get_attr: [my_instance, PublicIp] }

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@ -21,3 +21,5 @@ Template Guide
openstack openstack
cfn cfn
rackspace rackspace
hot_guide
hot_spec