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 Heat Orchestration Template (HOT) Guide.

Status

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.

Template structure

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
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.
parameter_groups
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.
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 with at least one resource should be defined in any HOT template, or the template would not really do anything when being instantiated.
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.
conditions

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.

Heat template 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:

2013-05-23

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

2014-10-16

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

2015-04-30

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

2015-10-15

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

2016-04-08

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

2016-10-14 | newton

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

2017-02-24 | ocata

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

Parameter groups section

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>
label
A human-readable label that defines the associated group of parameters.
description
This attribute allows for giving a human-readable description of the parameter group.
parameters
A list of parameters associated with this parameter group.
param name
The name of the parameter that is defined in the associated parameters section.

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>
param name
The name of the parameter.
type
The type of the parameter. Supported types are string, number, comma_delimited_list, json and boolean. This attribute is required.
label
A human readable name for the parameter. This attribute is optional.
description
A human readable description for the parameter. This attribute is optional.
default
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.
hidden

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.

constraints
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.
immutable
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.

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.

Parameter Constraints

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>
constraint type
Type of constraint to apply. The set of currently supported constraints is given below.
constraint definition
The actual constraint, depending on the constraint type. The concrete syntax for each constraint type is given below.
description
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.

length

The length constraint applies to parameters of type string. It defines a lower and upper limit for the length of the string value.

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.

range

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 }

modulo

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 }

allowed_values

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

allowed_pattern

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

custom_constraint

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

The following section lists the custom constraints and the plug-ins that support them.

Name Plug-in
barbican.container heat.engine.clients.os.barbican:ContainerConstraint
barbican.secret heat.engine.clients.os.barbican:SecretConstraint
cinder.backup heat.engine.clients.os.cinder:VolumeBackupConstraint
cinder.qos_specs heat.engine.clients.os.cinder:QoSSpecsConstraint
cinder.snapshot heat.engine.clients.os.cinder:VolumeSnapshotConstraint
cinder.volume heat.engine.clients.os.cinder:VolumeConstraint
cinder.vtype heat.engine.clients.os.cinder:VolumeTypeConstraint
cron_expression heat.engine.constraint.common_constraints:CRONExpressionConstraint
designate.domain heat.engine.clients.os.designate:DesignateDomainConstraint
dns_domain heat.engine.constraint.common_constraints:DNSDomainConstraint
dns_name heat.engine.constraint.common_constraints:DNSNameConstraint
expiration heat.engine.constraint.common_constraints:ExpirationConstraint
glance.image heat.engine.clients.os.glance:ImageConstraint
heat.resource_type heat.engine.constraint.heat_constraints:ResourceTypeConstraint
ip_addr heat.engine.constraint.common_constraints:IPConstraint
iso_8601 heat.engine.constraint.common_constraints:ISO8601Constraint
keystone.domain heat.engine.clients.os.keystone.keystone_constraints:KeystoneDomainConstraint
keystone.group heat.engine.clients.os.keystone.keystone_constraints:KeystoneGroupConstraint
keystone.project heat.engine.clients.os.keystone.keystone_constraints:KeystoneProjectConstraint
keystone.region heat.engine.clients.os.keystone.keystone_constraints:KeystoneRegionConstraint
keystone.role heat.engine.clients.os.keystone.keystone_constraints:KeystoneRoleConstraint
keystone.service heat.engine.clients.os.keystone.keystone_constraints:KeystoneServiceConstraint
keystone.user heat.engine.clients.os.keystone.keystone_constraints:KeystoneUserConstraint
mac_addr heat.engine.constraint.common_constraints:MACConstraint
magnum.baymodel heat.engine.clients.os.magnum:BaymodelConstraint
manila.share_network heat.engine.clients.os.manila:ManilaShareNetworkConstraint
manila.share_snapshot heat.engine.clients.os.manila:ManilaShareSnapshotConstraint
manila.share_type heat.engine.clients.os.manila:ManilaShareTypeConstraint
mistral.workflow heat.engine.clients.os.mistral:WorkflowConstraint
monasca.notification heat.engine.clients.os.monasca:MonascaNotificationConstraint
net_cidr heat.engine.constraint.common_constraints:CIDRConstraint
neutron.address_scope heat.engine.clients.os.neutron.neutron_constraints:AddressScopeConstraint
neutron.flow_classifier heat.engine.clients.os.neutron.neutron_constraints:FlowClassifierConstraint
neutron.lb.provider heat.engine.clients.os.neutron.neutron_constraints:LBaasV1ProviderConstraint
neutron.lbaas.listener heat.engine.clients.os.neutron.lbaas_constraints:ListenerConstraint
neutron.lbaas.loadbalancer heat.engine.clients.os.neutron.lbaas_constraints:LoadbalancerConstraint
neutron.lbaas.pool heat.engine.clients.os.neutron.lbaas_constraints:PoolConstraint
neutron.lbaas.provider heat.engine.clients.os.neutron.lbaas_constraints:LBaasV2ProviderConstraint
neutron.network heat.engine.clients.os.neutron.neutron_constraints:NetworkConstraint
neutron.port heat.engine.clients.os.neutron.neutron_constraints:PortConstraint
neutron.port_pair heat.engine.clients.os.neutron.neutron_constraints:PortPairConstraint
neutron.port_pair_group heat.engine.clients.os.neutron.neutron_constraints:PortPairGroupConstraint
neutron.qos_policy heat.engine.clients.os.neutron.neutron_constraints:QoSPolicyConstraint
neutron.router heat.engine.clients.os.neutron.neutron_constraints:RouterConstraint
neutron.security_group heat.engine.clients.os.neutron.neutron_constraints:SecurityGroupConstraint
neutron.subnet heat.engine.clients.os.neutron.neutron_constraints:SubnetConstraint
neutron.subnetpool heat.engine.clients.os.neutron.neutron_constraints:SubnetPoolConstraint
nova.flavor heat.engine.clients.os.nova:FlavorConstraint
nova.host heat.engine.clients.os.nova:HostConstraint
nova.keypair heat.engine.clients.os.nova:KeypairConstraint
nova.network heat.engine.clients.os.nova:NetworkConstraint
nova.server heat.engine.clients.os.nova:ServerConstraint
rel_dns_name heat.engine.constraint.common_constraints:RelativeDNSNameConstraint
sahara.image heat.engine.clients.os.sahara:ImageConstraint
sahara.plugin heat.engine.clients.os.sahara:PluginConstraint
senlin.cluster heat.engine.clients.os.senlin:ClusterConstraint
senlin.policy_type heat.engine.clients.os.senlin:PolicyTypeConstraint
senlin.profile heat.engine.clients.os.senlin:ProfileConstraint
senlin.profile_type heat.engine.clients.os.senlin:ProfileTypeConstraint
test_constr heat.engine.constraint.common_constraints:TestConstraintDelay
timezone heat.engine.constraint.common_constraints:TimezoneConstraint
trove.flavor heat.engine.clients.os.trove:FlavorConstraint

Pseudo parameters

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).

Resources section

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>
resource ID
A resource ID which must be unique within the resources section of the template.
type
The resource type, such as OS::Nova::Server or OS::Neutron::Port. This attribute is required.
properties
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.
metadata
Resource-specific metadata. This section is optional.
depends_on
Dependencies of the resource on one or more resources of the template. See Resource dependencies for details. This attribute is optional.
update_policy
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
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.
external_id
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

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

Resource dependencies

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

Outputs section

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>
parameter name
The output parameter name, which must be unique within the outputs section of a template.
description
A short description of the output parameter. This attribute is optional.
parameter value
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.
condition

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] }

Conditions section

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}
  ...
condition name
The condition name, which must be unique within the conditions section of a template.
expression

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

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.

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

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.

Intrinsic functions

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.

get_attr

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)
  - ...
resource name

The resource name for which the attribute needs to be resolved.

The resource name must exist in the resources section of the template.

attribute name
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>

get_file

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

get_param

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)
 - ...
parameter name
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.

get_resource

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 }

list_join

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.

digest

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>
algorithm
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.
value
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.

repeat

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>
template
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.
for_each
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.

resource_facade

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.

str_replace

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>
template
Defines the template string that contains placeholders which will be substituted at runtime.
params
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

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_split

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.

map_merge

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 {}.

map_replace

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.

yaql

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

equals

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.

if

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.

not

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.

and

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.

or

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.

filter

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].