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AWS Service Catalog Rule Functions

In the condition or assertions of a rule, you can use intrinsic functions, such as Fn::Equals, Fn::Not, and Fn::RefAll. The condition property determines if AWS CloudFormation applies the assertions. If the condition evaluates to true, AWS CloudFormation evaluates the assertions to verify whether a parameter value is valid when a provisioned product is created or updated. If a parameter values is invalid, AWS CloudFormation does not create or update the stack. If the condition evaluates to false, AWS CloudFormation doesn't check the parameter value and proceeds with the stack operation.

Fn::And

Returns true if all the specified conditions evaluate to true; returns false if any one of the conditions evaluates to false. Fn::And acts as an AND operator. The minimum number of conditions that you can include is two, and the maximum is ten.

Declaration

"Fn::And": [{condition}, {...}]

Parameters

condition

A rule-specific intrinsic function that evaluates to true or false.

Example

The following example evaluates to true if the referenced security group name is equal to sg-mysggroup and if the InstanceType parameter value is either m1.large or m1.small:

"Fn::And" : [ {"Fn::Equals" : ["sg-mysggroup", {"Ref" : "ASecurityGroup"}]}, {"Fn::Contains" : [["m1.large", "m1.small"], {"Ref" : "InstanceType"}]} ]

Fn::Contains

Returns true if a specified string matches at least one value in a list of strings.

Declaration

"Fn::Contains" : [[list_of_strings], string]

Parameters

list_of_strings

A list of strings, such as "A", "B", "C".

string

A string, such as "A", that you want to compare against a list of strings.

Example

The following function evaluates to true if the InstanceType parameter value is contained in the list (m1.large or m1.small):

"Fn::Contains" : [ ["m1.large", "m1.small"], {"Ref" : "InstanceType"} ]

Fn::EachMemberEquals

Returns true if a specified string matches all values in a list.

Declaration

"Fn::EachMemberEquals" : [[list_of_strings], string]

Parameters

list_of_strings

A list of strings, such as "A", "B", "C".

string

A string, such as "A", that you want to compare against a list of strings.

Example

The following function returns true if the Department tag for all parameters of type AWS::EC2::VPC::Id have a value of IT:

"Fn::EachMemberEquals" : [ {"Fn::ValueOfAll" : ["AWS::EC2::VPC::Id", "Tags.Department"]}, "IT" ]

Fn::EachMemberIn

Returns true if each member in a list of strings matches at least one value in a second list of strings.

Declaration

"Fn::EachMemberIn" : [[strings_to_check], strings_to_match]

Parameters

strings_to_check

A list of strings, such as "A", "B", "C". AWS CloudFormation checks whether each member in the strings_to_check parameter is in the strings_to_match parameter.

strings_to_match

A list of strings, such as "A", "B", "C". Each member in the strings_to_match parameter is compared against the members of the strings_to_check parameter.

Example

The following function checks whether users specify a subnet that is in a valid virtual private cloud (VPC). The VPC must be in the account and the region in which users are working with the stack. The function applies to all parameters of type AWS::EC2::Subnet::Id.

"Fn::EachMemberIn" : [ {"Fn::ValueOfAll" : ["AWS::EC2::Subnet::Id", "VpcId"]}, {"Fn::RefAll" : "AWS::EC2::VPC::Id"} ]

Fn::Equals

Compares two values to determine whether they are equal. Returns true if the two values are equal and false if they aren't.

Declaration

"Fn::Equals" : ["value_1", "value_2"]

Parameters

value

A value of any type that you want to compare with another value.

Example

The following example evaluates to true if the value for the EnvironmentType parameter is equal to prod:

"Fn::Equals" : [{"Ref" : "EnvironmentType"}, "prod"]

Fn::Not

Returns true for a condition that evaluates to false, and returns false for a condition that evaluates to true. Fn::Not acts as a NOT operator.

Declaration

"Fn::Not": [{condition}]

Parameters

condition

A rule-specific intrinsic function that evaluates to true or false.

Example

The following example evaluates to true if the value for the EnvironmentType parameter is not equal to prod:

"Fn::Not" : [{"Fn::Equals" : [{"Ref" : "EnvironmentType"}, "prod"]}]

Fn::Or

Returns true if any one of the specified conditions evaluates to true; returns false if all of the conditions evaluate to false. Fn::Or acts as an OR operator. The minimum number of conditions that you can include is two, and the maximum is ten.

Declaration

"Fn::Or": [{condition}, {...}]

Parameters

condition

A rule-specific intrinsic function that evaluates to true or false.

Example

The following example evaluates to true if the referenced security group name is equal to sg-mysggroup or if the InstanceType parameter value is either m1.large or m1.small:

"Fn::Or" : [ {"Fn::Equals" : ["sg-mysggroup", {"Ref" : "ASecurityGroup"}]}, {"Fn::Contains" : [["m1.large", "m1.small"], {"Ref" : "InstanceType"}]} ]

Fn::RefAll

Returns all values for a specified parameter type.

Declaration

"Fn::RefAll" : "parameter_type"

Parameters

parameter_type

An AWS-specific parameter type, such as AWS::EC2::SecurityGroup::Id or AWS::EC2::VPC::Id. For more information, see Parameters in the AWS CloudFormation User Guide.

Example

The following function returns a list of all VPC IDs for the region and AWS account in which the stack is being created or updated:

"Fn::RefAll" : "AWS::EC2::VPC::Id"

Fn::ValueOf

Returns an attribute value or list of values for a specific parameter and attribute.

Declaration

"Fn::ValueOf" : [ "parameter_logical_id", "attribute" ]

Parameters

attribute

The name of an attribute from which you want to retrieve a value. For more information about attributes, see Supported Attributes.

parameter_logical_id

The name of a parameter for which you want to retrieve attribute values. The parameter must be declared in the Parameters section of the template.

Examples

The following example returns the value of the Department tag for the VPC that is specified by the ElbVpc parameter:

"Fn::ValueOf" : ["ElbVpc", "Tags.Department"]

If you specify multiple values for a parameter, the Fn::ValueOf function can return a list. For example, you can specify multiple subnets and get a list of Availability Zones where each member is the Avalibility Zone of a particular subnet:

"Fn::ValueOf" : ["ListOfElbSubnets", "AvailabilityZone"]

Fn::ValueOfAll

Returns a list of all attribute values for a given parameter type and attribute.

Declaration

"Fn::ValueOfAll" : ["parameter_type", "attribute"]

Parameters

attribute

The name of an attribute from which you want to retrieve a value. For more information about attributes, see Supported Attributes.

parameter_type

An AWS-specific parameter type, such as AWS::EC2::SecurityGroup::Id or AWS::EC2::VPC::Id. For more information, see Parameters in the AWS CloudFormation User Guide.

Example

In the following example, the Fn::ValueOfAll function returns a list of values, where each member is the Department tag value for VPCs with that tag:

"Fn::ValueOfAll" : ["AWS::EC2::VPC::Id", "Tags.Department"]

Supported Functions

You cannot use another function within the Fn::ValueOf and Fn::ValueOfAll functions. However, you can use the following functions within all other rule-specific intrinsic functions:

  • Ref

  • Other rule-specific intrinsic functions

Supported Attributes

The following list describes the attribute values that you can retrieve for specific resources and parameter types:

The AWS::EC2::VPC::Id parameter type or VPC IDs
  • DefaultNetworkAcl

  • DefaultSecurityGroup

  • Tags.tag_key

The AWS::EC2::Subnet::Id parameter type or subnet IDs
  • AvailabilityZone

  • Tags.tag_key

  • VpcId

The AWS::EC2::SecurityGroup::Id parameter type or security group IDs
  • Tags.tag_key