This replaces any existing literal blocks containing template snippets with a yaml highlighted code block, which is more consistent with newer content. The resource HOT Syntax generation is also fixed to use yaml syntax highlighting by setting the rawsource argument Change-Id: Ie3404420ef70eba6402a4f7171cc56fb5a1f9445
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CloudFormation Compatible Functions
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::.
Ref
Returns the value of the named parameter or resource.
Parameters
- name : String
-
The name of the resource or parameter.
Usage
{Ref: my_server}
Returns the nova instance ID. For example,
d8093de0-850f-4513-b202-7979de6c0d55
.
Fn::Base64
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.
Parameters
- value : String
-
The string to convert.
Usage
{"Fn::Base64": "convert this string please."}
Returns the original input string.
Fn::FindInMap
Returns the value corresponding to keys into a two-level map declared in the Mappings section.
Parameters
- map_name : String
-
The logical name of a mapping declared in the Mappings section that contains the keys and values.
- top_level_key : String
-
The top-level key name. It's value is a list of key-value pairs.
- second_level_key : String
-
The second-level key name, which is set to one of the keys from the list assigned to top_level_key.
Usage
Mapping:
MyContacts:
jone: {phone: 337, email: a@b.com}
jim: {phone: 908, email: g@b.com}
{"Fn::FindInMap": ["MyContacts", "jim", "phone" ] }
Returns 908
.
Fn::GetAtt
Returns an attribute of a resource within the template.
Parameters
- resource : String
-
The name of the resource.
- attribute : String
-
The name of the attribute.
Usage
{Fn::GetAtt: [my_server, PublicIp]}
Returns an IP address such as 10.0.0.2
.
Fn::GetAZs
Returns the Availability Zones within the given region.
Note: AZ's and regions are not fully implemented in Heat.
Parameters
- region : String
-
The name of the region.
Usage
{Fn::GetAZs: ""}
Returns the list provided by
nova availability-zone-list
.
Fn::Join
Like python join, it joins a list of strings with the given delimiter.
Parameters
- delimiter : String
-
The string to join the list with.
- list : list
-
The list to join.
Usage
{Fn::Join: [",", ["beer", "wine", "more beer"]]}
Returns beer, wine, more beer
.
Fn::Select
Select an item from a list.
Heat extension: Select an item from a map
Parameters
- selector : string or integer
-
The number of item in the list or the name of the item in the map.
- collection : map or list
-
The collection to select the item from.
Usage
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
.
Fn::Split
This is the reverse of Join. Convert a string into a list based on the delimiter.
Parameters
- delimiter : string
-
Matching string to split on.
- string : String
-
The string to split.
Usage
{ "Fn::Split" : [ ",", "str1,str2,str3,str4"]}
Returns {["str1", "str2", "str3", "str4"]}
.
Fn::Replace
Find and replace one string with another.
Parameters
- substitutions : map
-
A map of substitutions.
- string: String
-
The string to do the substitutions in.
Usage
{"Fn::Replace": [
{'$var1': 'foo', '%var2%': 'bar'},
'$var1 is %var2%'
]}
Returns "foo is bar"
.
Fn::ResourceFacade
- 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.
Parameters
- attribute_name : String
-
One of
Metadata
,DeletionPolicy
orUpdatePolicy
.
Usage
{'Fn::ResourceFacade': 'Metadata'}
{'Fn::ResourceFacade': 'DeletionPolicy'}
{'Fn::ResourceFacade': 'UpdatePolicy'}
Example
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.
Fn::MemberListToMap
Convert an AWS style member list into a map.
Parameters
- 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.
Usage
{'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'}
.