NAME

Cfn - An object model for CloudFormation documents

DESCRIPTION

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:

Cfn object

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');

Constructors

new(Resources => { ... }, Outputs => { }, ...)

The default Moose constructor. You can initialize an empty document like this:

  my $cfn = Cfn->new;
  print $cfn->as_json;

from_hashref

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');

from_json

This method creates a Cfn object from a JSON string that contains a CloudFormation document in JSON format

from_yaml

This method creates a Cfn object from a YAML string that contains a CloudFormation document in YAML format

Attributes

json

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;

yaml

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.

cfn_options

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

AWSTemplateFormatVersion

A string with the value of the AWSTemplateFormatVersion field of the CloudFormation document. Can be undef.

Description

A string with the value of the Description field of the CloudFormation document. Can be undef.

Transform

An ArrayRef of Strings with the values of the Transform field of the CloudFormation document. Can be undef.

Parameters

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

Mappings

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

Conditions

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

Resources

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

Outputs

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

Metadata

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

Methods

as_hashref

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

as_json

Returns a JSON representation of the current instance

as_yaml

Returns a YAML representation of the current instance

path_to($path)

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.

resolve_dynamicvalues

Returns a new Cfn object with all Cfn::DynamicValues resolved.

ResourcesOfType($type)

Returns a list of all the Resources of a given type.

  foreach my $iam_user ($cfn->ResourcesOfType('AWS::IAM::User')) {
    ...
  }

addParameter($name, $object)

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));

addParameter($name, $type, %properties)

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);

addMapping($name, $object_or_hashref);

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

addOutput($name, $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' });

addOutput($name, $output[, %output_attributes]);

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');

addCondition($name, $value)

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

addResource($name, $object)

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.

addResource($name, $type, %properties)

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.

addResource($name, $name, $properties, $resource_attributes)

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.

addResourceMetadata($name, %metadata);

Adds metadata to the Metadata attribute of a Resource.

  $cfn->addResourceMetadata('R1', MyMetadataKey1 => 'Value');
  # $cfn->Resource('R1')->Metadata->{ MyMedataKey1 } is 'Value'

addDependsOn($resource_name, $depends_on1, $depends_on2)

  $cfn->addDependsOn('R1', 'R2', 'R3');
  # $cfn->Resource('R1')->DependsOn is [ 'R2', 'R3' ]

addDeletionPolicy($resource_name)

  Adds a DeletionPolicy to the resource. L<https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-deletionpolicy.html>

addUpdatePolicy($resource_name)

  Adds an UpdatePolicy to the resource. L<https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-updatepolicy.html>

Cfn::Value

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
  

Cfn::DynamicValue

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

Cfn::Value::Function

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

Cfn::Value::Function::Ref

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

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

Cfn::Value::Function::GetAtt

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'

Cfn::Value::Array

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.

Cfn::Value::Hash

This class represents JSON objects whose keys are not defined beforehand (arbitrary keys). It's Value property is a HashRef of Cfn::Values.

Cfn::Value::Primitive

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.

Cfn::Boolean

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.

Cfn::Integer

Used to store and validate CloudFormation Integer values.

Cfn::Long

Used to store and validate CloudFormation Long values.

Cfn::String

Used to store and validate CloudFormation String values.

Cfn::Double

Used to store and validate CloudFormation Double values.

Cfn::Timestamp

Used to store CloudFormation Timestamp values. Only validates that it's a string.

Cfn::Value::TypedValue

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.

Cfn::Resource

Represents a CloudFormation Resource. All Cfn::Resource::* objects (like Cfn::Resource::AWS::IAM::User) use Cfn::Resource as a base class.

Attributes for Cfn::Resource objects

The attributes for Cfn::Resource objects map to the attributes of CloudFormation Resources.

    {
      "Type": "AWS::IAM::User",
      "Properties": { ... },
      "DependsOn": "R2"
      ...
    }

Type

Holds a string with the type of the resource.

Properties

Holds a Cfn::Value::Properties subclass with the properties of the resource.

DeletionPolicy

Holds the DeletionPolicy. Validates that the DeletionPolicy is valid

DependsOn

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.

Condition

Can hold a String identifying the Condition property of a resource

Metadata

Is a Cfn::Value::Hash for the resources metadata

UpdatePolicy

Holds the UpdatePolicy. Validates that the UpdatePolicy is valid

CreationPolicy

HashRef with the CreationPolicy. Doesn't validate CreationPolicies.

Methods for Cfn::Resource objects

AttributeList

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>

supported_regions

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>

DependsOnList

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;

hasAttribute($attribute)

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

as_hashref

Like Cfn::Values, as_hashref returns a HashRef representation of the object ready for transforming to JSON.

Cfn::Resource::Properties

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.

Cfn::Parameter

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

Cfn::Parameter Attributes

Type

A string with the type of parameter. Validates that it's a CloudFormation supported parameter type.

Default

Holds the default value for the parameter

NoEcho

Holds the NoEcho property of the parameter

AllowedValues

An ArrayRef of the allowed values of the parameter

AllowedPattern

A String holding the pattern that the value of this parameter can take

MaxLength, MinLength, MaxValue, MinValue

Values holding the MaxLength, MinLength, MaxValue, MinValue of the parameter

Description

A string description of the parameter

ConstraintDescription

A string description of the constraint of the parameter

Cfn::Mapping

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.

Cfn::Output

Represents an output object in a CloudFormation document

Attributes for Cfn::Output objects

  "Outputs": {
    "Output1": {
      "Value": { "Ref": "Instance" }
    }
  }

Value

Holds the Value key of an output. Is a Cfn::Value

Description

Holds a String with the descrption of the output

Condition

Holds a String with the condition of the output

Export

Holds a HashRef with the export definition of the object

Methods for Cfn::Output objects

as_hashref

Returns a HashRef representation of the output that is convertible to JSON

STABILITY

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.

SEE ALSO

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-anatomy.html

This module kind of resembles troposphere (python): https://github.com/cloudtools/troposphere.

CLI utils

This distribution includes a series of CLI utilities to help you with CloudFormation:

cfn_list_resources [STRING]

Lists all the resources supported by Cfn. If a string is specified, will filter the ones matching the STRING.

cfn_region_matrix

Displays a table of what resource types are supported in each region

cfn_region_compatibility FILE

Takes a cloudformation template and calculates in what regions it will be deployable

cfn_resource_properties RESOURCE

Outputs information about a resource type: properties accessible via Fn::GetAtt, region availability and it's whole property structure.

AUTHOR

    Jose Luis Martinez
    CAPSiDE
    jlmartinez@capside.com

Contributions

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.

BUGS and SOURCE

The source code is located here: https://github.com/pplu/cfn-perl

Please report bugs to: https://github.com/pplu/cfn-perl/issues

COPYRIGHT and LICENSE

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.