Cfn - An object model for CloudFormation documents
This module helps parse, manipulate, validate and generate CloudFormation documents in JSON and YAML formats (see stability section for more information on YAML). It creates an object model of a CloudFormation template so you can work with the document as a set of objects. See https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-anatomy.html for more information.
It provides full blown objects for all know CloudFormation resources. See
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-template-resource-type-ref.html for a list
of all resource types. These objects live in the Cfn::Resource namespace.
The module provides a set of objects representing each piece of CloudFormation. Following is a list of all object types in the distribution:
The Cfn class is the "root" of a CloudFormation document. It represents an entire CloudFormation document.
It has attributes and methods to access the parts of a CloudFormation document.
use Cfn;
my $cfn = Cfn->new;
$cfn->addResource('MyRes' => ...);
my $res = $cfn->Resource('MyRes');
The default Moose constructor. You can initialize an empty document like this:
my $cfn = Cfn->new;
print $cfn->as_json;
CloudFormation documents resemble Perl HashRefs (since they're just JSON datastructures). This method converts a hashref that represents a CloudFormation document into a Cfn object.
use Data::Dumper;
my $cfn = Cfn->from_hashref({ Resources => { R1 => { Type => '...', Properties => { ... } } } });
print Dumper($cfn->Resource('R1');
This method creates a Cfn object from a JSON string that contains a CloudFormation document in JSON format
This method creates a Cfn object from a YAML string that contains a CloudFormation document in YAML format
When serializing to JSON with as_json, the encode method on this object is called passing the
documents hashref representation. By default the JSON generated is "ugly", that is, all in one line,
but in canonical form (so a given serialization always has attributes in the same order).
You can specify your own JSON serializer to control how JSON is generated:
my $cfn = Cfn->new(json => JSON->new->canonical->pretty);
...
print $cfn->as_json;
Holds a configured YAML::PP parser for use when serializing and deserializing to and from YAML.
Methods load_string and dump_string are called when needed from convert the object model
to a YAML document, and to convert a YAML document to a datastructure that can later be coerced
into the object model.
A Cfn::Internal::Options object instance that controls how the as_hashref method converts the Cfn object
to a datastructure suitable for CloudFormation (only HashRefs, ArrayRefs and Scalars).
You can specify your own options as a hashref with the attributes to Cfn::Internal::Options in the
constructor.
my $cfn = Cfn->new(cfn_options => { custom_resource_rename => 1 });
...
print Dumper($cfn->as_hashref);
See the Cfn::Internal::Options object for more details
A string with the value of the AWSTemplateFormatVersion field of the CloudFormation document. Can be undef.
A string with the value of the Description field of the CloudFormation document. Can be undef.
An ArrayRef of Strings with the values of the Transform field of the CloudFormation document. Can be undef.
A HashRef of Cfn::Parameter objects. The keys are the name of the Parameters.
There are a set of convenience methods for accessing this attribute:
$cfn->Parameter('ParamName') # returns a Cfn::Parameter or undef
$cfn->ParameterList # returns a list of the parameters in the document
$cfn->ParameterCount # returns the number of parameters in the document
A HashRef of Cfn::Mapping objects. The keys are the name of the Mappings.
There are a set of convenience methods for accessing this attribute:
$cfn->Mapping('MappingName') # returns a Cfn::Parameter or undef
$cfn->MappingList # returns a list of the mappings in the document
$cfn->MappingCount # returns the number of mappings in the document
A HashRef of Cfn::Condition objects. The keys are the name of the Mappings.
There are a set of convenience methods for accessing this attribute:
$cfn->Mapping('MappingName') # returns a Cfn::Mapping or undef
$cfn->MappingList # returns a list of the mappings in the document
$cfn->MappingCount # returns the number of mappings in the document
A HashRef of Cfn::Resource objects. The keys are the name of the Resources.
There are a set of convenience methods for accessing this attribute:
$cfn->Resource('ResourceName') # returns a Cfn::Resource or undef
$cfn->ResourceList # returns a list of the resources in the document
$cfn->ResourceCount # returns the number of resources in the document
A HashRef of Cfn::Output objects. The keys are the name of the Outputs.
There are a set of convenience methods for accessing this attribute:
$cfn->Output('OutputName') # returns a Cfn::Output or undef
$cfn->OutputList # returns a list of the outputs in the document
$cfn->OutputCount # returns the number of outputs in the document
A HashRef of Cfn::Value or subclasses of Cfn::Value. Represents the
Metadata key of the CloudFormation document.
There are a set of convenience methods for accessing this attribute:
$cfn->Metadata('MetadataName') # returns a Cfn::Metadata or undef
$cfn->MetadataList # returns a list of keys in the document Metadata
$cfn->MetadataCount # returns the number of keys in the document Metadata
Returns a Perl HashRef representation of the CloudFormation document. This HashRef has no objects in it. It is suitable for converting to JSON and passing to CloudFormation
as_hashref triggers the serialization process of the document, which scans the whole
object model asking it's components to serialize (calling their as_hashref). Objects
can decide how they serialize to a hashref.
When $cfn-as_hashref> is invoked, all the dynamic values in the Cfn object will be
called with the $cfn instance as the first parameter to their subroutine
$cfn->addResource('R1', 'AWS::IAM::User', Path => Cfn::DynamicValue->new(Value => sub {
my $cfn = shift;
return $cfn->ResourceCount + 41
}));
$cfn->as_hashref->{ Resources }->{ R1 }->{ Properties }->{ Path } # == 42
Returns a JSON representation of the current instance
Returns a YAML representation of the current instance
Given a path in the format 'Resources.R1.Properties.PropName' it will return the value
stored in PropName of the resource R1. Use 'Resource.R1.Properties.ArrayProp.0' to access
Arrays.
Returns a new Cfn object with all Cfn::DynamicValues resolved.
Returns a list of all the Resources of a given type.
foreach my $iam_user ($cfn->ResourcesOfType('AWS::IAM::User')) {
...
}
Adds an already instanced Cfn::Parameter object. Throws an exception if the parameter already exists.
$cfn->addParameter('P1', Cfn::Parameter->new(Type => 'String', MaxLength => 5));
Adds a named parameter to the document with the specified type and properties. See Cfn::Parameter for available
properties. Throws an exception if the parameter already exists.
$cfn->addParameter('P1', 'String', MaxLength => 5);
Adds a named mapping to the mappings of the document. The second parameter can be a Cfn::Mapping object or
a HashRef that will be coerced to a Cfn::Mapping object
$cfn->addMapping('amis', { 'eu-west-1' => 'ami-12345678' });
$cfn->addMapping('amis', Cfn::Mapping->new(Map => { 'eu-west-1' => 'ami-12345678' }));
# $cfn->Mapping('amis') is a Cfn::Mapping object
Adds an already instanced Cfn::Output object. Throws an exception if the output already exists.
$cfn->addParameter('O1', Cfn::Output->new(Value => { Ref => 'R1' });
Adds a named output to the document. See Cfn::Output for available
output_attributes. Throws an exception if the output already exists.
$cfn->addParameter('O1', { Ref => 'R1' });
$cfn->addParameter('O1', { Ref => 'R1' }, Description => 'Bla bla');
Adds a named condition to the document. The value parameter should be a HashRef that expresses a CloudFormation condition. See https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/conditions-section-structure.html
Adds a named resource to the document. $object has to be an instance of a
subclass of Cfn::Resource. Throws an exception if a resource already
exists with that name.
Adds a named resource to the document, putting the specified properties in the
resources properties. See subclasses of Cfn::Resource for more details.
$cfn->addResource('R1', 'AWS::IAM::User');
$cfn->addResource('R2', 'AWS::IAM::User', Path => '/');
# $cfn->Resource('R2')->Properties->Path is '/'
Throws an exception if a resource already exists with that name.
Adds a named resource to the document. properties and resource_attributes are hashrefs.
$cfn->addResource('R3', 'AWS::IAM::User', { Path => '/' });
# $cfn->Resource('R3')->Properties->Path is '/'
$cfn->addResource('R3', 'AWS::IAM::User', { Path => '/' }, { DependsOn => [ 'R2' ] });
# $cfn->Resource('R3')->DependsOn->[0] is 'R2'
Throws an exception if a resource already exists with that name.
Adds metadata to the Metadata attribute of a Resource.
$cfn->addResourceMetadata('R1', MyMetadataKey1 => 'Value');
# $cfn->Resource('R1')->Metadata->{ MyMedataKey1 } is 'Value'
$cfn->addDependsOn('R1', 'R2', 'R3');
# $cfn->Resource('R1')->DependsOn is [ 'R2', 'R3' ]
Adds a DeletionPolicy to the resource. L<https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-deletionpolicy.html>
Adds an UpdatePolicy to the resource. L<https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-updatepolicy.html>
Is a base class for the attributes of Cloudformation values. In Cloudformation you can find that in a resources attributes you can place functions, references, etc.
"Attribute": "hello"
"Attribute": { "Ref": "R1" }
"Attribute": { "Fn::GetAtt": [ "R1", "InstanceId" ] }
All value objects in the Cfn toolkit subclass Cfn::Value as a common ancestor. Once the object model is built,
you can find that a
$cfn->addResource('R1', 'AWS::IAM::User', Path => '/');
# $cfn->Resource('R1')->Properties->Path is a Cfn::Value::Primitive
$cfn->addResource('R1', 'AWS::IAM::User', Path => { 'Fn::Join' => [ '/', { Ref => 'Param1' }, '/' ] });
# $cfn->Resource('R1')->Properties->Path is a Cfn::Value::Function::Join
All Cfn::Value subclasses have to implement an as_hashref method that returns a HashRef suitable for
conversion to JSON for CloudFormation. A attributes of objects that hold Cfn::Value subclasses should
enable coercion of the attribute so that plain hashrefs can be coerced into the appropiate Cfn::Value objects
Here is a Hierarchy of the different Cfn::Value descendant object:
Cfn::Value
|--Cfn::DynamicValue
|--Cfn::Value::Function
| |--Cfn::Value::Function::Condition
| |--Cfn::Value::Function::Ref
| |--Cfn::Value::Function::PseudoParameter
| |--Cfn::Value::Function::GetAtt
|--Cfn::Value::Array
|--Cfn::Value::Hash
|--Cfn::Value::Primitive
| |--Cfn::Boolean
| |--Cfn::Integer
| |--Cfn::Long
| |--Cfn::String
| |--Cfn::Double
| |--Cfn::Timestamp
|--Cfn::Value::TypedValue
The Value attribute of this object is a CodeRef that get's called
when as_hashref is called.
$cfn->addResource('R1', 'AWS::IAM::User', Path => Cfn::DynamicValue->new(Value => sub { return 'Hello' });
$cfn->path_to('Resources.R1.Properties.Path') # isa Cfn::DynamicValue
$cfn->path_to('Resources.R1.Properties.Path')->as_hashref # eq 'Hello'
When $cfn-as_hashref> is invoked, all the dynamic values in the Cfn object will be
called with the $cfn instance as the first parameter to their subroutine
$cfn->addResource('R1', 'AWS::IAM::User', Path => Cfn::DynamicValue->new(Value => sub {
my $cfn = shift;
return $cfn->ResourceCount + 41
}));
$cfn->as_hashref->{ Resources }->{ R1 }->{ Properties }->{ Path } # == 42
All function statements derive from Cfn::Value::Function.
The name of the function can be found in the Function attribute
It's value can be found in the Value attribute
Object of this class represent a CloudFormation Ref. You can find the value
of the reference in the Value attribute. Note that the Value attribute contains
another Cfn::Value. It derives from Cfn::Value::Function
$cfn->addResource('R1', 'AWS::IAM::User', Path => { Ref => 'AWS::Region' });
$cfn->path_to('Resources.R1.Properties.Path') # isa Cfn::Value::Function::PseudoParameter
This is a subclass of Cfn::Value::Function::Ref used to hold what CloudFormation
calls PseudoParameters.
$cfn->addResource('R1', 'AWS::IAM::User', Path => { Ref => 'AWS::Region' });
$cfn->path_to('Resources.R1.Properties.Path') # isa Cfn::Value::Function::PseudoParam
This class represents 'Fn::GetAtt' nodes in the object model. It's a subclass of Cfn::Value::Function.
$cfn->addResource('R1', 'AWS::IAM::User', Path => { 'Fn::GetAtt' => [ 'R1', 'InstanceId' ] });
$cfn->path_to('Resources.R1.Properties.Path') # isa Cfn::Value::Function::GetAtt
$cfn->path_to('Resources.R1.Properties.Path')->LogicalId # eq 'R1'
$cfn->path_to('Resources.R1.Properties.Path')->Property # eq 'InstanceId'
This class represents Arrays in the object model. It's Value property is an ArrayRef
of Cfn::Values or Cfn::Resource::Properties.
There is also a subtype called Cfn::Value::ArrayOfPrimitives that restricts the values
in the array to Cfn::Value::Primitive types.
This class represents JSON objects whose keys are not defined beforehand (arbitrary keys).
It's Value property is a HashRef of Cfn::Values.
This is a base class for any "simple" value (what the CloudFormation spec calls PrimitiveType).
This classes Value attribute has no type constraint, so it actually accepts anything. This class
is supposed to only be inherited from, specializing the Value attribute to a specific type.
Used to store and validate CloudFormation Boolean values. Has a stringy attribute that controls if as_hashref
returns a string boolean "true" or "false" or a literal true or false, since these two
boolean forms are accepted in CloudFormation.
Used to store and validate CloudFormation Integer values.
Used to store and validate CloudFormation Long values.
Used to store and validate CloudFormation String values.
Used to store and validate CloudFormation Double values.
Used to store CloudFormation Timestamp values. Only validates that it's a string.
Used as a base class for structured properties of CloudFormation resources. The subclasses of TypedValue declare Moose attributes that are used to represent and validate that the properties of a CloudFormation resource are well formed.
Represents a CloudFormation Resource. All Cfn::Resource::* objects (like Cfn::Resource::AWS::IAM::User)
use Cfn::Resource as a base class.
The attributes for Cfn::Resource objects map to the attributes of CloudFormation Resources.
{
"Type": "AWS::IAM::User",
"Properties": { ... },
"DependsOn": "R2"
...
}
Holds a string with the type of the resource.
Holds a Cfn::Value::Properties subclass with the properties of the resource.
Holds the DeletionPolicy. Validates that the DeletionPolicy is valid
Can hold either a single string or an arrayref of strings. This is because CloudFormation
supports DependsOn in these two forms. Method DependsOnList provides a uniform way
of accessing the DependsOn attribute.
Can hold a String identifying the Condition property of a resource
Is a Cfn::Value::Hash for the resources metadata
Holds the UpdatePolicy. Validates that the UpdatePolicy is valid
HashRef with the CreationPolicy. Doesn't validate CreationPolicies.
Returns an ArrayRef of attributes that can be recalled in CloudFormation via Fn::GetAtt.
Can also be retrieved as a class method Cfn::Resource::...-AttributeList>
Returns an ArrayRef of the AWS regions where the resource can be provisioned.
Can also be retrieved as a class method Cfn::Resource::...-supported_regions>
Returns a list of dependencies from the DependsOn attribute (it doesn't matter if the DependsOn attribute is a String or an ArrayRef of Strings.
my @deps = $cfn->Resource('R1')->DependsOnList;
Returns true if the specified attribute is in the AttributeList. Note that some resources
(AWS::CloudFormation::CustomResource) can return true for values that are not in AttributeList
Like Cfn::Values, as_hashref returns a HashRef representation of the object ready
for transforming to JSON.
A base class for the objects that the Properties attribute of Cfn::Resources hold.
Subclasses of Cfn::Resource::Properties are used to validate and represent the properties
of resources inside the object model. See Cfn::Resource::Properties::AWS::IAM::User for
an example.
Each subclass of Cfn::Resource::Properties has to have attributes to hold the values of
the properties of the resource it represents.
Represents a Parameter in a CloudFormation document
my $cfn = Cfn->new;
$cfn->addParameter('P1', 'String', Default => 5);
$cfn->Parameter('P1')->Default # 5
$cfn->Parameter('P1')->NoEcho # undef
A string with the type of parameter. Validates that it's a CloudFormation supported parameter type.
Holds the default value for the parameter
Holds the NoEcho property of the parameter
An ArrayRef of the allowed values of the parameter
A String holding the pattern that the value of this parameter can take
Values holding the MaxLength, MinLength, MaxValue, MinValue of the parameter
A string description of the parameter
A string description of the constraint of the parameter
This object represents the value of the Mappings key in a CloudFormation
document. It has a Map attribute to hold the Mappings in the CloudFormation
document.
Represents an output object in a CloudFormation document
"Outputs": {
"Output1": {
"Value": { "Ref": "Instance" }
}
}
Holds the Value key of an output. Is a Cfn::Value
Holds a String with the descrption of the output
Holds a String with the condition of the output
Holds a HashRef with the export definition of the object
Returns a HashRef representation of the output that is convertible to JSON
YAML support is recent, and due to the still evolving YAML::PP module, may break (altough the tests are there to detect that). This distribution will try to keep up as hard as it can with latest YAML::PP developments.
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-anatomy.html
This module kind of resembles troposphere (python): https://github.com/cloudtools/troposphere.
This distribution includes a series of CLI utilities to help you with CloudFormation:
Lists all the resources supported by Cfn. If a string is specified, will filter the ones matching the STRING.
Displays a table of what resource types are supported in each region
Takes a cloudformation template and calculates in what regions it will be deployable
Outputs information about a resource type: properties accessible via Fn::GetAtt, region availability and it's whole property structure.
Jose Luis Martinez
CAPSiDE
jlmartinez@capside.com
Thanks to Sergi Pruneda, Miquel Ruiz, Luis Alberto Gimenez, Eleatzar Colomer, Oriol Soriano, Roi Vazquez for years of work on this module.
TINITA for helping make the YAML support possible. First for the YAML::PP module, which is the only Perl module to support sufficiently modern YAML features, and also for helping me in the use of YAML::PP.
The source code is located here: https://github.com/pplu/cfn-perl
Please report bugs to: https://github.com/pplu/cfn-perl/issues
Copyright (c) 2013 by CAPSiDE This code is distributed under the Apache 2 License. The full text of the license can be found in the LICENSE file included with this module.