There are a number of functions that you can use to help you write CloudFormation compatible templates. While most CloudFormation functions are supported in HOT version '2013-05-23', Fn::Select is the only CloudFormation function supported in HOT templates since version '2014-10-16' which is introduced in Juno. All of these functions (except Ref) start with Fn::.

Returns the value of the named parameter or resource.

name The name of the resource or parameter.

{Ref: my_server} Returns the nova instance ID. For example, d8093de0-850f-4513-b202-7979de6c0d55.

This is a placeholder for a function to convert an input string to Base64. This function in Heat actually performs no conversion. It is included for the benefit of CFN templates that convert UserData to Base64. Heat only accepts UserData in plain text.

value The string to convert.

{"Fn::Base64": "convert this string please."} Returns the original input string.

Returns the value corresponding to keys into a two-level map declared in the Mappings section.

map_name The logical name of a mapping declared in the Mappings section that contains the keys and values. top_level_key The top-level key name. It's value is a list of key-value pairs. second_level_key The second-level key name, which is set to one of the keys from the list assigned to top_level_key.

Mapping: MyContacts: jone: {phone: 337, email: a@b.com} jim: {phone: 908, email: g@b.com} {"Fn::FindInMap": ["MyContacts", "jim", "phone" ] } Returns 908.

Returns an attribute of a resource within the template.

resource The name of the resource. attribute The name of the attribute.

{Fn::GetAtt: [my_server, PublicIp]} Returns an IP address such as 10.0.0.2.

Returns the Availability Zones within the given region. Note: AZ's and regions are not fully implemented in Heat.

region The name of the region.

{Fn::GetAZs: ""} Returns the list provided by nova availability-zone-list.

Like python join, it joins a list of strings with the given delimiter.

delimiter The string to join the list with. list The list to join.

{Fn::Join: [",", ["beer", "wine", "more beer"]]} Returns beer, wine, more beer.

Select an item from a list. Heat extension: Select an item from a map

selector The number of item in the list or the name of the item in the map. collection The collection to select the item from.

For a list lookup: { "Fn::Select" : [ "2", [ "apples", "grapes", "mangoes" ] ] } Returns mangoes. For a map lookup: { "Fn::Select" : [ "red", {"red": "a", "flu": "b"} ] } Returns a.

This is the reverse of Join. Convert a string into a list based on the delimiter.

delimiter Matching string to split on. string The string to split.

{ "Fn::Split" : [ ",", "str1,str2,str3,str4"]} Returns {["str1", "str2", "str3", "str4"]}.

Find and replace one string with another.

substitutions A map of substitutions. string: String The string to do the substitutions in.

{"Fn::Replace": [ {'$var1': 'foo', '%var2%': 'bar'}, '$var1 is %var2%' ]} Returns "foo is bar".

When writing a Template Resource: user writes a template that will fill in for a resource (the resource is the facade). when they are writing their template they need to access the metadata from the facade.

attribute_name One of Metadata, DeletionPolicy or UpdatePolicy.

{'Fn::ResourceFacade': 'Metadata'} {'Fn::ResourceFacade': 'DeletionPolicy'} {'Fn::ResourceFacade': 'UpdatePolicy'}

Here is a top level template top.yaml resources: my_server: type: OS::Nova::Server metadata: key: value some: more stuff Here is a resource template my_actual_server.yaml resources: _actual_server_: type: OS::Nova::Server metadata: {'Fn::ResourceFacade': Metadata} The environment file env.yaml resource_registry: resources: my_server: "OS::Nova::Server": my_actual_server.yaml To use it $ heat stack-create -f top.yaml -e env.yaml What happened is the metadata in top.yaml (key: value, some: more stuff) gets passed into the resource template via the Fn::ResourceFacade function.

Convert an AWS style member list into a map.

key name: string The name of the key (normally "Name" or "Key"). value name: string The name of the value (normally "Value"). list: A list of strings The string to convert.

{'Fn::MemberListToMap': ['Name', 'Value', ['.member.0.Name=key', '.member.0.Value=door', '.member.1.Name=colour', '.member.1.Value=green']]} Returns {'key': 'door', 'colour': 'green'}.