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 Heat Orchestration Template (HOT) Guide.
HOT is considered reliable, supported, and standardized as of our Icehouse (April 2014) release. The Heat core team may make improvements to the standard, which very likely would be backward compatible. The template format is also versioned. Since Juno release, Heat supports multiple different versions of the HOT specification.
HOT templates are defined in YAML and follow the structure outlined below.
heat_template_version: 2016-10-14
description:
# a description of the template
parameter_groups:
# a declaration of input parameter groups and order
parameters:
# declaration of input parameters
resources:
# declaration of template resources
outputs:
# declaration of output parameters
conditions:
# declaration of conditions
This key with value 2013-05-23
(or a later date) indicates that the
YAML document is a HOT template of the specified version.
This optional key allows for giving a description of the template, or the workload that can be deployed using the template.
This section allows for specifying how the input parameters should be grouped and the order to provide the parameters in. This section is optional and can be omitted when necessary.
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.
This section contains the declaration of the single resources of the template. This section with at least one resource should be defined in any HOT template, or the template would not really do anything when being instantiated.
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.
This optional section includes statements which can be used to restrict
when a resource is created or when a property is defined. They can be
associated with resources and resource properties in the
resources
section, also can be associated with outputs in the
outputs
sections of a template.
Note: Support for this section is added in the Newton version.
The value of heat_template_version
tells Heat not only the format of the
template but also features that will be validated and supported. Beginning with
the Newton release, the version can be either the date of the Heat release or
the code name of the Heat release. Heat currently supports the following values
for the heat_template_version
key:
The key with value 2013-05-23
indicates that the YAML document is a HOT
template and it may contain features implemented until the Icehouse
release. This version supports the following functions (some are back
ported to this version):
get_attr
get_file
get_param
get_resource
list_join
resource_facade
str_replace
Fn::Base64
Fn::GetAZs
Fn::Join
Fn::MemberListToMap
Fn::Replace
Fn::ResourceFacade
Fn::Select
Fn::Split
Ref
The key with value 2014-10-16
indicates that the YAML document is a HOT
template and it may contain features added and/or removed up until the Juno
release. This version removes most CFN functions that were supported in
the Icehouse release, i.e. the 2013-05-23
version. So the supported
functions now are:
get_attr
get_file
get_param
get_resource
list_join
resource_facade
str_replace
Fn::Select
The key with value 2015-04-30
indicates that the YAML document is a HOT
template and it may contain features added and/or removed up until the Kilo
release. This version adds the repeat
function. So the complete list of
supported functions is:
get_attr
get_file
get_param
get_resource
list_join
repeat
digest
resource_facade
str_replace
Fn::Select
The key with value 2015-10-15
indicates that the YAML document is a HOT
template and it may contain features added and/or removed up until the
Liberty release. This version removes the Fn::Select function, path based
get_attr
/get_param
references should be used instead. Moreover
get_attr
since this version returns dict of all attributes for the
given resource excluding show attribute, if there’s no <attribute name>
specified, e.g. { get_attr: [<resource name>]}
. This version
also adds the str_split function and support for passing multiple lists to
the existing list_join function. The complete list of supported functions
is:
get_attr
get_file
get_param
get_resource
list_join
repeat
digest
resource_facade
str_replace
str_split
The key with value 2016-04-08
indicates that the YAML document is a HOT
template and it may contain features added and/or removed up until the
Mitaka release. This version also adds the map_merge
function which
can be used to merge the contents of maps. The complete list of supported
functions is:
digest
get_attr
get_file
get_param
get_resource
list_join
map_merge
repeat
resource_facade
str_replace
str_split
The key with value 2016-10-14
or newton
indicates that the YAML
document is a HOT template and it may contain features added and/or removed
up until the Newton release. This version adds the yaql
function which
can be used for evaluation of complex expressions, the map_replace
function that can do key/value replacements on a mapping, and the if
function which can be used to return corresponding value based on condition
evaluation. The complete list of supported functions is:
digest
get_attr
get_file
get_param
get_resource
list_join
map_merge
map_replace
repeat
resource_facade
str_replace
str_split
yaql
if
This version adds equals
condition function which can be used
to compare whether two values are equal, the not
condition function
which acts as a NOT operator, the and
condition function which acts
as an AND operator to evaluate all the specified conditions, the or
condition function which acts as an OR operator to evaluate all the
specified conditions. The complete list of supported condition
functions is:
equals
get_param
not
and
or
The key with value 2017-02-24
or ocata
indicates that the YAML
document is a HOT template and it may contain features added and/or removed
up until the Ocata release. This version adds the str_replace_strict
function which raises errors for missing params and the filter
function
which filters out values from lists. The complete list of supported
functions is:
digest
filter
get_attr
get_file
get_param
get_resource
list_join
map_merge
map_replace
repeat
resource_facade
str_replace
str_replace_strict
str_split
yaql
if
The complete list of supported condition functions is:
equals
get_param
not
and
or
The key with value 2017-09-01
or pike
indicates that the YAML
document is a HOT template and it may contain features added and/or removed
up until the Pike release. This version adds the make_url
function for
assembling URLs, the list_concat
function for combining multiple
lists, the list_concat_unique
function for combining multiple
lists without repeating items, the string_replace_vstrict
function
which raises errors for missing and empty params, and the contains
function which checks whether specific value is in a sequence. The
complete list of supported functions is:
digest
filter
get_attr
get_file
get_param
get_resource
list_join
make_url
list_concat
list_concat_unique
contains
map_merge
map_replace
repeat
resource_facade
str_replace
str_replace_strict
str_replace_vstrict
str_split
yaql
if
We support ‘yaql’ and ‘contains’ as condition functions in this version. The complete list of supported condition functions is:
equals
get_param
not
and
or
yaql
contains
The key with value 2018-03-02
or queens
indicates that the YAML
document is a HOT template and it may contain features added and/or removed
up until the Queens release. The complete list of supported functions is:
digest
filter
get_attr
get_file
get_param
get_resource
list_join
make_url
list_concat
list_concat_unique
contains
map_merge
map_replace
repeat
resource_facade
str_replace
str_replace_strict
str_replace_vstrict
str_split
yaql
if
The complete list of supported condition functions is:
equals
get_param
not
and
or
yaql
contains
The key with value 2018-08-31
or rocky
indicates that the YAML
document is a HOT template and it may contain features added and/or removed
up until the Rocky release. The complete list of supported functions is:
digest
filter
get_attr
get_file
get_param
get_resource
list_join
make_url
list_concat
list_concat_unique
contains
map_merge
map_replace
repeat
resource_facade
str_replace
str_replace_strict
str_replace_vstrict
str_split
yaql
if
The complete list of supported condition functions is:
equals
get_param
not
and
or
yaql
contains
The key with value 2021-04-16
or wallaby
indicates that the YAML
document is a HOT template and it may contain features added and/or removed
up until the Wallaby release.
This version adds a 2-argument variant of the if
function. When the
condition is false and no third argument is supplied, the entire enclosing item
(which may be e.g. a list item, a key-value pair in a dict, or a property
value) will be elided. This allows for e.g. conditional definition of
properties while keeping the default value when the condition is false.
The complete list of supported functions is:
digest
filter
get_attr
get_file
get_param
get_resource
list_join
make_url
list_concat
list_concat_unique
contains
map_merge
map_replace
repeat
resource_facade
str_replace
str_replace_strict
str_replace_vstrict
str_split
yaql
if
The complete list of supported condition functions is:
equals
get_param
not
and
or
yaql
contains
The parameter_groups
section allows for specifying how the input parameters
should be grouped and the order to provide the parameters in. These groups are
typically used to describe expected behavior for downstream user interfaces.
These groups are specified in a list with each group containing a list of
associated parameters. The lists are used to denote the expected order of the
parameters. Each parameter should be associated to a specific group only once
using the parameter name to bind it to a defined parameter in the
parameters
section.
parameter_groups:
- label: <human-readable label of parameter group>
description: <description of the parameter group>
parameters:
- <param name>
- <param name>
A human-readable label that defines the associated group of parameters.
This attribute allows for giving a human-readable description of the parameter group.
A list of parameters associated with this parameter group.
The name of the parameter that is defined in the associated 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 | boolean>
label: <human-readable name of the parameter>
description: <description of the parameter>
default: <default value for parameter>
hidden: <true | false>
constraints:
<parameter constraints>
immutable: <true | false>
tags: <list of parameter categories>
The name of the parameter.
The type of the parameter. Supported types
are string
, number
, comma_delimited_list
, json
and
boolean
.
This attribute is required.
A human readable name for the parameter. This attribute is optional.
A human readable description for the parameter. This attribute is optional.
A default value for the parameter. This value is used if the user doesn’t specify his own value during deployment. This attribute is optional.
Defines whether the parameters should be hidden when a user requests information about a stack created from the template. This attribute can be used to hide passwords specified as parameters.
This attribute is optional and defaults to false
.
A list of constraints to apply. The constraints are validated by the Orchestration engine when a user deploys a stack. The stack creation fails if the parameter value doesn’t comply to the constraints. This attribute is optional.
Defines whether the parameter is updatable. Stack update fails, if this is
set to true
and the parameter value is changed.
This attribute is optional and defaults to false
.
A list of strings to specify the category of a parameter. This value is used to categorize a parameter so that users can group the parameters. This attribute is optional.
The table below describes all currently supported types with examples:
Type |
Description |
Examples |
---|---|---|
string |
A literal string. |
“String param” |
number |
An integer or float. |
“2”; “0.2” |
comma_delimited_list |
An array of literal strings that are separated by commas. The total number of strings should be one more than the total number of commas. |
[“one”, “two”]; “one, two”; Note: “one, two” returns [“one”, “ two”] |
json |
A JSON-formatted map or list. |
{“key”: “value”} |
boolean |
Boolean type value, which can be equal “t”, “true”, “on”, “y”, “yes”, or “1” for true value and “f”, “false”, “off”, “n”, “no”, or “0” for false value. |
“on”; “n” |
The following example shows a minimalistic definition of two parameters
parameters:
user_name:
type: string
label: User Name
description: User name to be configured for the application
port_number:
type: number
label: Port Number
description: Port number to be configured for the web server
Note
The description and the label are optional, but defining these attributes is good practice to provide useful information about the role of the parameter to the user.
The constraints
block of a parameter definition defines
additional validation constraints that apply to the value of the
parameter. The parameter values provided by a user are validated against the
constraints at instantiation time. The constraints are defined as a list with
the following syntax
constraints:
- <constraint type>: <constraint definition>
description: <constraint description>
Type of constraint to apply. The set of currently supported constraints is given below.
The actual constraint, depending on the constraint type. The concrete syntax for each constraint type is given below.
A description of the constraint. The text is presented to the user when the value he defines violates the constraint. If omitted, a default validation message is presented to the user. This attribute is optional.
The following example shows 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 to present useful messages to the user at deployment time.
parameters:
user_name:
type: string
label: User Name
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
Note
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.
The following sections list the supported types of parameter constraints, along with the concrete syntax for each type.
The length
constraint applies to parameters of type
string
, comma_delimited_list
and json
.
It defines a lower and upper limit for the length of the string value or list/map collection.
The syntax of 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.
The range
constraint applies to parameters of type number
.
It defines 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 and 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 }
The modulo
constraint applies to parameters of type number
. The value
is valid if it is a multiple of step
, starting with offset
.
The syntax of the modulo
constraint is
modulo: { step: <step>, offset: <offset> }
Both step
and offset
must be specified.
For example, the following modulo constraint would only allow for odd numbers
modulo: { step: 2, offset: 1 }
The allowed_values
constraint applies to parameters of type
string
or number
. It specifies 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 list.
The syntax of the allowed_values
constraint is
allowed_values: [ <value>, <value>, ... ]
Alternatively, the following YAML list notation can be used
allowed_values:
- <value>
- <value>
- ...
For example
parameters:
instance_type:
type: string
label: Instance Type
description: Instance type for compute instances
constraints:
- allowed_values:
- m1.small
- m1.medium
- m1.large
The allowed_pattern
constraint applies to parameters of type
string
. It specifies 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
label: User Name
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
The custom_constraint
constraint adds an extra step of validation,
generally to check that the specified resource exists in the backend. Custom
constraints get implemented by plug-ins and can provide any kind of advanced
constraint validation logic.
The syntax of the custom_constraint
constraint is
custom_constraint: <name>
The name
attribute specifies the concrete type of custom constraint. It
corresponds to the name under which the respective validation plugin has been
registered in the Orchestration engine.
For example
parameters:
key_name
type: string
description: SSH key pair
constraints:
- custom_constraint: nova.keypair
In addition to parameters defined by a template author, Heat also
creates three parameters for every stack that allow referential access
to the stack’s name, stack’s identifier and project’s
identifier. These parameters are named OS::stack_name
for the
stack name, OS::stack_id
for the stack identifier and
OS::project_id
for the project identifier. These values are
accessible via the get_param intrinsic function, just like
user-defined parameters.
Note
OS::project_id
is available since 2015.1 (Kilo).
The resources
section defines actual resources that make up a stack
deployed from the HOT template (for instance compute instances, networks,
storage volumes).
Each resource is defined as a separate block in the resources
section with
the following syntax
resources:
<resource ID>:
type: <resource type>
properties:
<property name>: <property value>
metadata:
<resource specific metadata>
depends_on: <resource ID or list of ID>
update_policy: <update policy>
deletion_policy: <deletion policy>
external_id: <external resource ID>
condition: <condition name or expression or boolean>
A resource ID which must be unique within the resources
section of the
template.
The resource type, such as OS::Nova::Server
or OS::Neutron::Port
.
This attribute is required.
A list of resource-specific properties. The property value can be provided in place, or via a function (see Intrinsic functions). This section is optional.
Resource-specific metadata. This section is optional.
Dependencies of the resource on one or more resources of the template. See Resource dependencies for details. This attribute is optional.
Update policy for the resource, in the form of a nested dictionary. Whether update policies are supported and what the exact semantics are depends on the type of the current resource. This attribute is optional.
Deletion policy for the resource. The allowed deletion policies are
Delete
, Retain
, and Snapshot
. Beginning with
heat_template_version
2016-10-14
, the lowercase equivalents
delete
, retain
, and snapshot
are also allowed.
This attribute is optional; the default policy is to delete the physical
resource when deleting a resource from the stack.
Allows for specifying the resource_id for an existing external (to the stack) resource. External resources can not depend on other resources, but we allow other resources depend on external resource. This attribute is optional. Note: when this is specified, properties will not be used for building the resource and the resource is not managed by Heat. This is not possible to update that attribute. Also resource won’t be deleted by heat when stack is deleted.
Condition for the resource. Which decides whether to create the resource or not. This attribute is optional.
Note: Support condition
for resource is added in the Newton version.
Depending on the type of resource, the resource block might include more resource specific data.
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.
The following example demonstrates the definition of a simple compute resource with some fixed property values
resources:
my_instance:
type: OS::Nova::Server
properties:
flavor: m1.small
image: F18-x86_64-cfntools
The depends_on
attribute of a resource defines a dependency between this
resource and one or more other resources.
If a resource depends on just one other resource, the ID of the other resource
is specified as string of the depends_on
attribute, as shown in the
following example
resources:
server1:
type: OS::Nova::Server
depends_on: server2
server2:
type: OS::Nova::Server
If a resource depends on more than one other resources, the value of the
depends_on
attribute is specified as a list of resource IDs, as shown in
the following example
resources:
server1:
type: OS::Nova::Server
depends_on: [ server2, server3 ]
server2:
type: OS::Nova::Server
server3:
type: OS::Nova::Server
The outputs
section defines output parameters that should be available to
the user after a stack has been created. This would be, for example, parameters
such as IP addresses of deployed instances, or URLs of web applications
deployed as part of a stack.
Each output parameter is defined as a separate block within the outputs section according to the following syntax
outputs:
<parameter name>:
description: <description>
value: <parameter value>
condition: <condition name or expression or boolean>
The output parameter name, which must be unique within the outputs
section of a template.
A short description of the output parameter. This attribute is optional.
The value of the output parameter. This value is usually resolved by means of a function. See Intrinsic functions for details about the functions. This attribute is required.
To conditionally define an output value. None value will be shown if the condition is False. This attribute is optional.
Note: Support condition
for output is added in the Newton version.
The example below shows how the IP address of a compute resource can be defined as an output parameter
outputs:
instance_ip:
description: IP address of the deployed compute instance
value: { get_attr: [my_instance, first_address] }
The conditions
section defines one or more conditions which are evaluated
based on input parameter values provided when a user creates or updates a
stack. The condition can be associated with resources, resource properties and
outputs. For example, based on the result of a condition, user can
conditionally create resources, user can conditionally set different values
of properties, and user can conditionally give outputs of a stack.
The conditions
section is defined with the following syntax
conditions:
<condition name1>: {expression1}
<condition name2>: {expression2}
...
The condition name, which must be unique within the conditions
section of a template.
The expression which is expected to return True or False. Usually, the condition functions can be used as expression to define conditions:
equals
get_param
not
and
or
yaql
Note: In condition functions, you can reference a value from an input parameter, but you cannot reference resource or its attribute. We support referencing other conditions (by condition name) in condition functions. We support ‘yaql’ as condition function in the Pike version.
An example of conditions section definition
conditions:
cd1: True
cd2:
get_param: param1
cd3:
equals:
- get_param: param2
- yes
cd4:
not:
equals:
- get_param: param3
- yes
cd5:
and:
- equals:
- get_param: env_type
- prod
- not:
equals:
- get_param: zone
- beijing
cd6:
or:
- equals:
- get_param: zone
- shanghai
- equals:
- get_param: zone
- beijing
cd7:
not: cd4
cd8:
and:
- cd1
- cd2
cd9:
yaql:
expression: $.data.services.contains('heat')
data:
services:
get_param: ServiceNames
cd10:
contains:
- 'neutron'
- get_param: ServiceNames
The example below shows how to associate condition with resources
parameters:
env_type:
default: test
type: string
conditions:
create_prod_res: {equals : [{get_param: env_type}, "prod"]}
resources:
volume:
type: OS::Cinder::Volume
condition: create_prod_res
properties:
size: 1
The ‘create_prod_res’ condition evaluates to true if the ‘env_type’ parameter is equal to ‘prod’. In the above sample template, the ‘volume’ resource is associated with the ‘create_prod_res’ condition. Therefore, the ‘volume’ resource is created only if the ‘env_type’ is equal to ‘prod’.
The example below shows how to conditionally define an output
outputs:
vol_size:
value: {get_attr: [my_volume, size]}
condition: create_prod_res
In the above sample template, the ‘vol_size’ output is associated with the ‘create_prod_res’ condition. Therefore, the ‘vol_size’ output is given corresponding value only if the ‘env_type’ is equal to ‘prod’, otherwise the value of the output is None.
HOT provides a set of intrinsic functions that can be used inside templates to perform specific tasks, such as getting the value of a resource attribute at runtime. The following section describes the role and syntax of the intrinsic functions.
Note: these functions can only be used within the “properties” section of each resource or in the outputs section.
The get_attr
function references an attribute of a
resource. The attribute value is resolved at runtime using the resource
instance created from the respective resource definition.
Path based attribute referencing using keys or indexes requires
heat_template_version
2014-10-16
or higher.
The syntax of the get_attr
function is
get_attr:
- <resource name>
- <attribute name>
- <key/index 1> (optional)
- <key/index 2> (optional)
- ...
The resource name for which the attribute needs to be resolved.
The resource name must exist in the resources
section of the template.
The attribute name to be resolved. If the attribute returns a complex data structure such as a list or a map, then subsequent keys or indexes can be specified. These additional parameters are used to navigate the data structure to return the desired value.
The following example demonstrates how to use the get_attr
function:
resources:
my_instance:
type: OS::Nova::Server
# ...
outputs:
instance_ip:
description: IP address of the deployed compute instance
value: { get_attr: [my_instance, first_address] }
instance_private_ip:
description: Private IP address of the deployed compute instance
value: { get_attr: [my_instance, networks, private, 0] }
In this example, if the networks
attribute contained the following data:
{"public": ["2001:0db8:0000:0000:0000:ff00:0042:8329", "1.2.3.4"],
"private": ["10.0.0.1"]}
then the value of get_attr
function would resolve to 10.0.0.1
(first item of the private
entry in the networks
map).
From heat_template_version
: ‘2015-10-15’ <attribute_name> is optional and
if <attribute_name> is not specified, get_attr
returns dict of all
attributes for the given resource excluding show attribute. In this case
syntax would be next:
get_attr:
- <resource_name>
The get_file
function returns the content of a file into the template.
It is generally used as a file inclusion mechanism for files
containing scripts or configuration files.
The syntax of get_file
function is
get_file: <content key>
The content key
is used to look up the files
dictionary that is
provided in the REST API call. The Orchestration client command
(heat
) is get_file
aware and populates the files
dictionary with the actual content of fetched paths and URLs. The
Orchestration client command supports relative paths and transforms these
to the absolute URLs required by the Orchestration API.
Note
The get_file
argument must be a static path or URL and not rely on
intrinsic functions like get_param
. the Orchestration client does not
process intrinsic functions (they are only processed by the Orchestration
engine).
The example below demonstrates the get_file
function usage with both
relative and absolute URLs
resources:
my_instance:
type: OS::Nova::Server
properties:
# general properties ...
user_data:
get_file: my_instance_user_data.sh
my_other_instance:
type: OS::Nova::Server
properties:
# general properties ...
user_data:
get_file: http://example.com/my_other_instance_user_data.sh
The files
dictionary generated by the Orchestration client during
instantiation of the stack would contain the following keys:
file:///path/to/my_instance_user_data.sh
http://example.com/my_other_instance_user_data.sh
The get_param
function references an input parameter of a template. It
resolves to the value provided for this input parameter at runtime.
The syntax of the get_param
function is
get_param:
- <parameter name>
- <key/index 1> (optional)
- <key/index 2> (optional)
- ...
The parameter name to be resolved. If the parameters returns a complex data structure such as a list or a map, then subsequent keys or indexes can be specified. These additional parameters are used to navigate the data structure to return the desired value.
The following example demonstrates the use of the get_param
function
parameters:
instance_type:
type: string
label: Instance Type
description: Instance type to be used.
server_data:
type: json
resources:
my_instance:
type: OS::Nova::Server
properties:
flavor: { get_param: instance_type}
metadata: { get_param: [ server_data, metadata ] }
key_name: { get_param: [ server_data, keys, 0 ] }
In this example, if the instance_type
and server_data
parameters
contained the following data:
{"instance_type": "m1.tiny",
{"server_data": {"metadata": {"foo": "bar"},
"keys": ["a_key","other_key"]}}}
then the value of the property flavor
would resolve to m1.tiny
,
metadata
would resolve to {"foo": "bar"}
and key_name
would resolve
to a_key
.
The get_resource
function references another resource within the
same template. At runtime, it is resolved to reference the ID of the referenced
resource, which is resource type specific. For example, a reference to a
floating IP resource returns the respective IP address at runtime. The syntax
of the get_resource
function is
get_resource: <resource ID>
The resource ID of the referenced resource is given as single parameter to the
get_resource
function.
For example
resources:
instance_port:
type: OS::Neutron::Port
properties: ...
instance:
type: OS::Nova::Server
properties:
...
networks:
port: { get_resource: instance_port }
The list_join
function joins a list of strings with the given delimiter.
The syntax of the list_join
function is
list_join:
- <delimiter>
- <list to join>
For example
list_join: [', ', ['one', 'two', 'and three']]
This resolve to the string one, two, and three
.
From HOT version 2015-10-15
you may optionally pass additional lists, which
will be appended to the previous lists to join.
For example:
list_join: [', ', ['one', 'two'], ['three', 'four']]
This resolve to the string one, two, three, four
.
From HOT version 2015-10-15
you may optionally also pass non-string list
items (e.g json/map/list parameters or attributes) and they will be serialized
as json before joining.
The digest
function allows for performing digest operations on a given
value. This function has been introduced in the Kilo release and is usable with
HOT versions later than 2015-04-30
.
The syntax of the digest
function is
digest:
- <algorithm>
- <value>
The digest algorithm. Valid algorithms are the ones provided natively by hashlib (md5, sha1, sha224, sha256, sha384, and sha512) or any one provided by OpenSSL.
The value to digest. This function will resolve to the corresponding hash of the value.
For example
# from a user supplied parameter
pwd_hash: { digest: ['sha512', { get_param: raw_password }] }
The value of the digest function would resolve to the corresponding hash of
the value of raw_password
.
The repeat
function allows for dynamically transforming lists by iterating
over the contents of one or more source lists and replacing the list elements
into a template. The result of this function is a new list, where the elements
are set to the template, rendered for each list item.
The syntax of the repeat
function is
repeat:
template:
<template>
for_each:
<var>: <list>
The template
argument defines the content generated for each iteration,
with placeholders for the elements that need to be replaced at runtime.
This argument can be of any supported type.
The for_each
argument is a dictionary that defines how to generate the
repetitions of the template and perform substitutions. In this dictionary
the keys are the placeholder names that will be replaced in the template,
and the values are the lists to iterate on. On each iteration, the function
will render the template by performing substitution with elements of the
given lists. If a single key/value pair is given in this argument, the
template will be rendered once for each element in the list. When more
than one key/value pairs are given, the iterations will be performed on all
the permutations of values between the given lists. The values in this
dictionary can be given as functions such as get_attr
or get_param
.
The following example shows how a security group resource can be defined to include a list of ports given as a parameter
parameters:
ports:
type: comma_delimited_list
label: ports
default: "80,443,8080"
resources:
security_group:
type: OS::Neutron::SecurityGroup
properties:
name: web_server_security_group
rules:
repeat:
for_each:
<%port%>: { get_param: ports }
template:
protocol: tcp
port_range_min: <%port%>
port_range_max: <%port%>
The following example demonstrates how the use of multiple lists enables the security group to also include parameterized protocols
parameters:
ports:
type: comma_delimited_list
label: ports
default: "80,443,8080"
protocols:
type: comma_delimited_list
label: protocols
default: "tcp,udp"
resources:
security_group:
type: OS::Neutron::SecurityGroup
properties:
name: web_server_security_group
rules:
repeat:
for_each:
<%port%>: { get_param: ports }
<%protocol%>: { get_param: protocols }
template:
protocol: <%protocol%>
port_range_min: <%port%>
Note how multiple entries in the for_each
argument are equivalent to
nested for-loops in most programming languages.
From HOT version 2016-10-14
you may also pass a map as value for the
for_each
key, in which case the list of map keys will be used as value.
From HOT version 2017-09-01
(or pike) you may specify a argument
permutations
to decide whether to iterate nested the over all the
permutations of the elements in the given lists. If ‘permutations’ is not
specified, we set the default value to true to compatible with before behavior.
The args have to be lists instead of dicts if ‘permutations’ is False because
keys in a dict are unordered, and the list args all have to be of the
same length.
parameters:
subnets:
type: comma_delimited_list
label: subnets
default: "sub1, sub2"
networks:
type: comma_delimited_list
label: networks
default: "net1, net2"
resources:
my_server:
type: OS::Nova:Server
properties:
networks:
repeat:
for_each:
<%sub%>: { get_param: subnets }
<%net%>: { get_param: networks }
template:
subnet: <%sub%>
network: <%net%>
permutations: false
After resolved, we will get the networks of server like: [{subnet: sub1, network: net1}, {subnet: sub2, network: net2}]
The resource_facade
function retrieves data in a parent
provider template.
A provider template provides a custom definition of a resource, called its
facade. For more information about custom templates, see Template composition.
The syntax of the resource_facade
function is
resource_facade: <data type>
data type
can be one of metadata
, deletion_policy
or
update_policy
.
The str_replace
function dynamically constructs strings by
providing a template string with placeholders and a list of mappings to assign
values to those placeholders at runtime. The placeholders are replaced with
mapping values wherever a mapping key exactly matches a placeholder.
The syntax of the str_replace
function is
str_replace:
template: <template string>
params: <parameter mappings>
Defines the template string that contains placeholders which will be substituted at runtime.
Provides parameter mappings in the form of dictionary. Each key refers to a
placeholder used in the template
attribute. From HOT version
2015-10-15
you may optionally pass non-string parameter values
(e.g json/map/list parameters or attributes) and they will be serialized
as json before replacing, prior heat/HOT versions require string values.
The following example shows a simple use of the str_replace
function in the
outputs section of a template to build a URL for logging into a deployed
application
resources:
my_instance:
type: OS::Nova::Server
# general metadata and properties ...
outputs:
Login_URL:
description: The URL to log into the deployed application
value:
str_replace:
template: http://host/MyApplication
params:
host: { get_attr: [ my_instance, first_address ] }
The following examples show the use of the str_replace
function to build an instance initialization script
parameters:
DBRootPassword:
type: string
label: Database Password
description: Root password for MySQL
hidden: true
resources:
my_instance:
type: OS::Nova::Server
properties:
# general properties ...
user_data:
str_replace:
template: |
#!/bin/bash
echo "Hello world"
echo "Setting MySQL root password"
mysqladmin -u root password $db_rootpassword
# do more things ...
params:
$db_rootpassword: { get_param: DBRootPassword }
In the example above, one can imagine that MySQL is being configured on a
compute instance and the root password is going to be set based on a user
provided parameter. The script for doing this is provided as userdata to the
compute instance, leveraging the str_replace
function.
str_replace_strict
behaves identically to the str_replace
function, only an error is raised if any of the params are not present
in the template. This may help catch typo’s or other issues sooner
rather than later when processing a template.
str_replace_vstrict
behaves identically to the
str_replace_strict
function, only an error is raised if any of the
params are empty. This may help catch issues (i.e., prevent
resources from being created with bogus values) sooner rather than later if
it is known that all the params should be non-empty.
The str_split
function allows for splitting a string into a list by
providing an arbitrary delimiter, the opposite of list_join
.
The syntax of the str_split
function is as follows:
str_split:
- ','
- string,to,split
Or:
str_split: [',', 'string,to,split']
The result of which is:
['string', 'to', 'split']
Optionally, an index may be provided to select a specific entry from the
resulting list, similar to get_attr
/get_param
:
str_split: [',', 'string,to,split', 0]
The result of which is:
'string'
Note: The index starts at zero, and any value outside the maximum (e.g the length of the list minus one) will cause an error.
The map_merge
function merges maps together. Values in the latter maps
override any values in earlier ones. Can be very useful when composing maps
that contain configuration data into a single consolidated map.
The syntax of the map_merge
function is
map_merge:
- <map 1>
- <map 2>
- ...
For example
map_merge: [{'k1': 'v1', 'k2': 'v2'}, {'k1': 'v2'}]
This resolves to a map containing {'k1': 'v2', 'k2': 'v2'}
.
Maps containing no items resolve to {}.
The map_replace
function does key/value replacements on an existing mapping.
An input mapping is processed by iterating over all keys/values and performing
a replacement if an exact match is found in either of the optional keys/values
mappings.
The syntax of the map_replace
function is
map_replace:
- <input map>
- keys: <map of key replacements>
values: <map of value replacements>
For example
map_replace:
- k1: v1
k2: v2
- keys:
k1: K1
values:
v2: V2
This resolves to a map containing {'K1': 'v1', 'k2': 'V2'}
.
The keys/values mappings are optional, either or both may be specified.
Note that an error is raised if a replacement defined in “keys” results in a collision with an existing keys in the input or output map.
Also note that while unhashable values (e.g lists) in the input map are valid, they will be ignored by the values replacement, because no key can be defined in the values mapping to define their replacement.
The yaql
evaluates yaql expression on a given data.
The syntax of the yaql
function is
yaql:
expression: <expression>
data: <data>
For example
parameters:
list_param:
type: comma_delimited_list
default: [1, 2, 3]
outputs:
max_elem:
value:
yaql:
expression: $.data.list_param.select(int($)).max()
data:
list_param: {get_param: list_param}
max_elem output will be evaluated to 3
The equals
function compares whether two values are equal.
The syntax of the equals
function is
equals: [value_1, value_2]
The value can be any type that you want to compare. This function returns true if the two values are equal or false if they aren’t.
For example
equals: [{get_param: env_type}, 'prod']
If param ‘env_type’ equals to ‘prod’, this function returns true, otherwise returns false.
The if
function returns the corresponding value based on the
evaluation of a condition.
The syntax of the if
function is
if: [condition_name, value_if_true, value_if_false]
For example
conditions:
create_prod_res: {equals : [{get_param: env_type}, "prod"]}
resources:
test_server:
type: OS::Nova::Server
properties:
name: {if: ["create_prod_res", "s_prod", "s_test"]}
The ‘name’ property is set to ‘s_prod’ if the condition “create_prod_res” evaluates to true (if parameter ‘env_type’ is ‘prod’), and is set to ‘s_test’ if the condition “create_prod_res” evaluates to false (if parameter ‘env_type’ isn’t ‘prod’).
Note: You define all conditions in the conditions
section of a
template except for if
conditions. You can use the if
condition
in the property values in the resources
section and outputs
sections
of a template.
Beginning with the wallaby
template version, the third argument is
optional. If only two arguments are passed, the entire enclosing item is
removed when the condition is false.
For example:
conditions:
override_name: {not: {equals: [{get_param: server_name}, ""]}}
resources:
test_server:
type: OS::Nova::Server
properties:
name: {if: [override_name, {get_param: server_name}]}
In this example, the default name for the server (which is generated by Heat
when the property value is not specified) would be used when the
server_name
parameter value is an empty string.
The not
function acts as a NOT operator.
The syntax of the not
function is
not: condition
Note: A condition can be an expression such as equals
, or
and and
that evaluates to true or false, can be a boolean, and can be other condition
name defined in conditions
section of template.
Returns true for a condition that evaluates to false or returns false for a condition that evaluates to true.
For example
not:
equals:
- get_param: env_type
- prod
If param ‘env_type’ equals to ‘prod’, this function returns false, otherwise returns true.
Another example with boolean value definition
not: True
This function returns false.
Another example reference other condition name
not: my_other_condition
This function returns false if my_other_condition evaluates to true, otherwise returns true.
The and
function acts as an AND operator to evaluate all the
specified conditions.
The syntax of the and
function is
and: [{condition_1}, {condition_2}, ... {condition_n}]
Note: A condition can be an expression such as equals
, or
and not
that evaluates to true or false, can be a boolean, and can be other condition
names defined in conditions
section of template.
Returns true if all the specified conditions evaluate to true, or returns false if any one of the conditions evaluates to false.
For example
and:
- equals:
- get_param: env_type
- prod
- not:
equals:
- get_param: zone
- beijing
If param ‘env_type’ equals to ‘prod’, and param ‘zone’ is not equal to ‘beijing’, this function returns true, otherwise returns false.
Another example reference with other conditions
and:
- other_condition_1
- other_condition_2
This function returns true if other_condition_1 and other_condition_2 evaluate to true both, otherwise returns false.
The or
function acts as an OR operator to evaluate all the
specified conditions.
The syntax of the or
function is
or: [{condition_1}, {condition_2}, ... {condition_n}]
Note: A condition can be an expression such as equals
, and
and not
that evaluates to true or false, can be a boolean, and can be other condition
names defined in conditions
section of template.
Returns true if any one of the specified conditions evaluate to true, or returns false if all of the conditions evaluates to false.
For example
or:
- equals:
- get_param: env_type
- prod
- not:
equals:
- get_param: zone
- beijing
If param ‘env_type’ equals to ‘prod’, or the param ‘zone’ is not equal to ‘beijing’, this function returns true, otherwise returns false.
Another example reference other conditions
or:
- other_condition_1
- other_condition_2
This function returns true if any one of other_condition_1 or other_condition_2 evaluate to true, otherwise returns false.
The filter
function removes values from lists.
The syntax of the filter
function is
filter:
- <values>
- <list>
For example
parameters:
list_param:
type: comma_delimited_list
default: [1, 2, 3]
outputs:
output_list:
value:
filter:
- [3]
- {get_param: list_param}
output_list will be evaluated to [1, 2].
The make_url
function builds URLs.
The syntax of the make_url
function is
make_url:
scheme: <protocol>
username: <username>
password: <password>
host: <hostname or IP>
port: <port>
path: <path>
query:
<key1>: <value1>
<key2>: <value2>
fragment: <fragment>
All parameters are optional.
For example
outputs:
server_url:
value:
make_url:
scheme: http
host: {get_attr: [server, networks, <network_name>, 0]}
port: 8080
path: /hello
query:
recipient: world
fragment: greeting
server_url
will be evaluated to a URL in the form:
http://[<server IP>]:8080/hello?recipient=world#greeting
The list_concat
function concatenates lists together.
The syntax of the list_concat
function is
list_concat:
- <list #1>
- <list #2>
- ...
For example
list_concat: [['v1', 'v2'], ['v3', 'v4']]
Will resolve to the list ['v1', 'v2', 'v3', 'v4']
.
Null values will be ignored.
The list_concat_unique
function behaves identically to the function
list_concat
, only removes the repeating items of lists.
For example
list_concat_unique: [['v1', 'v2'], ['v2', 'v3']]
Will resolve to the list ['v1', 'v2', 'v3']
.
The contains
function checks whether the specific value is
in a sequence.
The syntax of the contains
function is
contains: [<value>, <sequence>]
This function returns true if value is in sequence or false if it isn’t.
For example
contains: ['v1', ['v1', 'v2', 'v3']]
Will resolve to boolean true.
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