Heat Orchestration Template (HOT) specification¶

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

2017-09-01 | pike¶

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`` which raises errors for missing and empty params, and the contains 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

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

The following sections list the supported types of parameter constraints, along with the concrete syntax for each type.

length: { min: <lower limit>, max: <upper limit> }

range: { min: <lower limit>, max: <upper limit> }

range: { min: 0, max: 10 }

modulo: { step: <step>, offset: <offset> }

modulo: { step: 2, offset: 1 }

allowed_values: [ <value>, <value>, ... ]

allowed_values:
  - <value>
  - <value>
  - ...

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: <regular expression>

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: <name>

parameters:
  key_name
    type: string
    description: SSH key pair
    constraints:
      - custom_constraint: nova.keypair

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.

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

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.

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.

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}]

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_replace_vstrict¶

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.

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].

make_url¶

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

list_concat¶

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.

list_concat_unique¶

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', 'v43']]

Will resolve to the list ['v1', 'v2', 'v3'].

contains¶

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.