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Constructs for implementing CDK custom resources

Project description

CDK Custom Resources


Stability: Experimental

This is a developer preview (public beta) module. Releases might lack important features and might have future breaking changes.

This API is still under active development and subject to non-backward compatible changes or removal in any future version. Use of the API is not recommended in production environments. Experimental APIs are not subject to the Semantic Versioning model.


This module is part of the AWS Cloud Development Kit project.

AWS Custom Resource

Sometimes a single API call can fill the gap in the CloudFormation coverage. In this case you can use the AwsCustomResource construct. This construct creates a custom resource that can be customized to make specific API calls for the CREATE, UPDATE and DELETE events. Additionally, data returned by the API call can be extracted and used in other constructs/resources (creating a real CloudFormation dependency using Fn::GetAtt under the hood).

The physical id of the custom resource can be specified or derived from the data returned by the API call.

The AwsCustomResource uses the AWS SDK for JavaScript. Services, actions and parameters can be found in the API documentation.

Path to data must be specified using a dot notation, e.g. to get the string value of the Title attribute for the first item returned by dynamodb.query it should be Items.0.Title.S.

Examples

Verify a domain with SES:

const verifyDomainIdentity = new AwsCustomResource(this, 'VerifyDomainIdentity', {
  onCreate: {
    service: 'SES',
    action: 'verifyDomainIdentity',
    parameters: {
      Domain: 'example.com'
    },
    physicalResourceIdPath: 'VerificationToken' // Use the token returned by the call as physical id
  }
});

new route53.TxtRecord(zone, 'SESVerificationRecord', {
  recordName: `_amazonses.example.com`,
  recordValue: verifyDomainIdentity.getData('VerificationToken')
});

Get the latest version of a secure SSM parameter:

const getParameter = new AwsCustomResource(this, 'GetParameter', {
  onUpdate: { // will also be called for a CREATE event
    service: 'SSM',
    action: 'getParameter',
    parameters: {
      Name: 'my-parameter',
      WithDecryption: true
    },
    physicalResourceId: Date.now().toString() // Update physical id to always fetch the latest version
  }
});

// Use the value in another construct with
getParameter.getData('Parameter.Value')

IAM policy statements required to make the API calls are derived from the calls and allow by default the actions to be made on all resources (*). You can restrict the permissions by specifying your own list of statements with the policyStatements prop.

Chained API calls can be achieved by creating dependencies:

const awsCustom1 = new AwsCustomResource(this, 'API1', {
  onCreate: {
    service: '...',
    action: '...',
    physicalResourceId: '...'
  }
});

const awsCustom2 = new AwsCustomResource(this, 'API2', {
  onCreate: {
    service: '...',
    action: '...'
    parameters: {
      text: awsCustom1.getData('Items.0.text')
    },
    physicalResourceId: '...'
  }
})

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