The AWS::CloudFormation::CustomResource resource creates a custom resource. Custom resources provide a way for you to write custom provisioning logic into your CloudFormation templates and have CloudFormation run it anytime you create, update (if you changed the custom resource), or delete a stack.
For more information, see Create custom provisioning logic with custom resources in the AWS CloudFormation User Guide.
NoteIf you use AWS PrivateLink, custom resources in the VPC must have access to CloudFormation-specific Amazon S3 buckets. Custom resources must send responses to a presigned Amazon S3 URL. If they can't send responses to Amazon S3, CloudFormation won't receive a response and the stack operation fails. For more information, see Access CloudFormation using an interface endpoint (AWS PrivateLink) in the AWS CloudFormation User Guide.
SyntaxTo declare this entity in your AWS CloudFormation template, use the following syntax:
PropertiesServiceTimeout
The maximum time, in seconds, that can elapse before a custom resource operation times out.
The value must be an integer from 1 to 3600. The default value is 3600 seconds (1 hour).
Required: No
Type: String
Update requires: No interruption
ServiceToken
The service token, such as an Amazon SNS topic ARN or Lambda function ARN. The service token must be from the same Region as the stack.
Updates aren't supported.
Required: Yes
Type: String
Update requires: Replacement
The Fn::GetAtt intrinsic function returns a value for a specified attribute of this type. The following are the available attributes and sample return values.
For more information about using the Fn::GetAtt intrinsic function, see Fn::GetAtt.
Specifying custom resource type names
For custom resources, you can specify AWS::CloudFormation::CustomResource as the resource type, or you can specify your own resource type name. For example, instead of using AWS::CloudFormation::CustomResource, you can use Custom::MyCustomResourceTypeName.
Custom resource type names can include alphanumeric characters and the following characters: _@-. You can specify a custom resource type name up to a maximum length of 60 characters. You can't change the type during an update.
Using your own resource type names helps you quickly differentiate the types of custom resources in your stack. For example, if you had two custom resources that conduct two different ping tests, you could name their type as Custom::PingTester to make them easily identifiable as ping testers (instead of using AWS::CloudFormation::CustomResource).
Replacing a custom resource during an update
You can update custom resources that require a replacement of the underlying physical resource. When you update a custom resource in a CloudFormation template, CloudFormation sends an update request to that custom resource. If the custom resource requires a replacement, the new custom resource must send a response with the new physical ID. When CloudFormation receives the response, it compares the PhysicalResourceId between the old and new custom resources. If they're different, CloudFormation recognizes the update as a replacement and sends a delete request to the old resource. For more information about updating custom resources, see Amazon SNS-backed custom resources in the AWS CloudFormation User Guide.
For information about monitoring the progress of the update, see Monitor stack progress in the AWS CloudFormation User Guide.
Retrieving return values
For a custom resource, return values are defined by the custom resource provider, and are retrieved by calling Fn::GetAtt on the provider-defined attributes.
The following example demonstrates how to create a custom resource definition in a template.
JSON{
"AWSTemplateFormatVersion": "2010-09-09",
"Resources": {
"MyFrontEndTest": {
"Type": "Custom::PingTester",
"Version": "1.0",
"Properties": {
"ServiceToken": "arn:aws:sns:us-west-2:123456789012:CRTest",
"ServiceTimeout": "600",
"key1": "string",
"key2": [
"list"
],
"key3": {
"key4": "map"
}
}
}
},
"Outputs": {
"CustomResourceAttribute1": {
"Value": {
"Fn::GetAtt": [
"MyFrontEndTest",
"responseKey1"
]
}
},
"CustomResourceAttribute2": {
"Value": {
"Fn::GetAtt": [
"MyFrontEndTest",
"responseKey2"
]
}
}
}
}AWSTemplateFormatVersion: 2010-09-09
Resources:
MyFrontEndTest:
Type: 'Custom::PingTester'
Version: '1.0'
Properties:
ServiceToken: 'arn:aws:sns:us-west-2:123456789012:CRTest'
ServiceTimeout: 600
key1: string
key2:
- list
key3:
key4: map
Outputs:
CustomResourceAttribute1:
Value: !GetAtt
- MyFrontEndTest
- responseKey1
CustomResourceAttribute2:
Value: !GetAtt
- MyFrontEndTest
- responseKey2
With Lambda functions and custom resources, you can run custom code in response to stack events (create, update, and delete). The following custom resource invokes a Lambda function and sends it the StackName property as input. The function uses this property to get outputs from the appropriate stack.
{
"MyCustomResource": {
"Type": "Custom::TestLambdaCrossStackRef",
"Properties": {
"ServiceToken": {
"Fn::Join": [
"",
[
"arn:aws:lambda:",
{
"Ref": "AWS::Region"
},
":",
{
"Ref": "AWS::AccountId"
},
":function:",
{
"Ref": "LambdaFunctionName"
}
]
]
},
"ServiceTimeout": "35",
"StackName": {
"Ref": "NetworkStackName"
}
}
}
}MyCustomResource:
Type: 'Custom::TestLambdaCrossStackRef'
Properties:
ServiceToken: !Join
- ''
- - 'arn:aws:lambda:'
- !Ref 'AWS::Region'
- ':'
- !Ref 'AWS::AccountId'
- ':function:'
- !Ref LambdaFunctionName
ServiceTimeout: 35
StackName: !Ref NetworkStackNameRetroSearch is an open source project built by @garambo | Open a GitHub Issue
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