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.
{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.
Returns the value corresponding to keys into a two-level map declared in the Mappings section.
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.
Returns the Availability Zones within the given region.
Note: AZ’s and regions are not fully implemented in Heat.
Like python join, it joins a list of strings with the given delimiter.
Select an item from a list.
Heat extension: Select an item from a map
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.
Find and replace one string with another.
{"Fn::Replace": [
{'$var1': 'foo', '%var2%': 'bar'},
'$var1 is %var2%'
]}
Returns "foo is bar"
.
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
$ openstack stack create -t top.yaml -e env.yaml mystack
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.
{'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'}
.
Compares whether two values are equal. And returns true if the two values are equal or false if they aren’t.
{'Fn::Equals': [{'Ref': 'env_type'}, 'prod']}
Returns true if the param ‘env_type’ equals to ‘prod’, otherwise returns false.
Returns one value if the specified condition evaluates to true and another value if the specified condition evaluates to false.
Conditions
section.{'Fn::If': ['create_prod', 'value_true', 'value_false']}
Returns ‘value_true’ if the condition ‘create_prod’ evaluates to true, otherwise returns ‘value_false’.
Acts as a NOT operator.
The syntax of the Fn::Not
function is
{'Fn::Not': [condition]}
Returns true for a condition that evaluates to false or returns false for a condition that evaluates to true.
Fn::Equals
that evaluates to true or false
can be defined in this function, also we can set a boolean value
as a condition.{'Fn::Not': [{'Fn::Equals': [{'Ref': env_type'}, 'prod']}]}
Returns false if the param ‘env_type’ equals to ‘prod’, otherwise returns true.
Acts as an AND operator to evaluate all the specified conditions. Returns true if all the specified conditions evaluate to true, or returns false if any one of the conditions evaluates to false.
{'Fn::And': [{'Fn::Equals': [{'Ref': env_type}, 'prod']},
{'Fn::Not': [{'Fn::Equals': [{'Ref': zone}, 'beijing']}]}]
Returns true if the param ‘env_type’ equals to ‘prod’ and the param ‘zone’ is not equal to ‘beijing’, otherwise returns false.
Acts as an OR operator to evaluate all the specified conditions. Returns true if any one of the specified conditions evaluate to true, or returns false if all of the conditions evaluates to false.
{'Fn::Or': [{'Fn::Equals': [{'Ref': zone}, 'shanghai']},
{'Fn::Equals': [{'Ref': zone}, 'beijing']}]}
Returns true if the param ‘zone’ equals to ‘shanghai’ or ‘beijing’, otherwise returns false.
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