Skip to main content

Implement custom AWS CloudFormation resources with Python Lambda functions.

Project description

Implement custom AWS CloudFormation resources with Python Lambda functions.

This helps you reference non-AWS resources within CloudFormation - for instance, let’s get a StatusCake alert in our stack:

Type: Custom::StatusCakeTest
Version: 1.0
Properties:
  WebsiteName: vitalwebsite.com
  WebsiteURL: http://vitalwebsite.com
  CheckRate: 300
  TestType: HTTP

(Implementation left as an exercise for the reader)

See also

  • Sample code in the examples directory.
  • AWS docs

Lambda Handler

Here’s a simple resource:

from custom_resource import BaseHandler

class Handler(BaseHandler):
    def create(self, event, context):
        return "CreatedId", {"AndSome": "MetaData"}

    def update(self, event, context):
        return "UpdatedId", {"AndSome": "MetaData"}

    def delete(self, event, context):
        return "DeletedId", {"AndSome": "MetaData"}

handler = Handler()

We extend the BaseHandler class, and implement create, update and delete methods. All of these methods are required.

The methods must either:

  • Return a string representing a resource ID. This can be used within your CFN template via the Ref function.
  • Return a resource ID string, and a dict containing strings for keys and values. These key/value pairs can be used with the GetAtt function.
  • Return a custom_resource.Success or custom_resource.Failed object.
  • Return a custom_resource.Defer object, signifying you’ll process this asynchronously. See async responses below.
  • Raise an exception.

BaseHandler will respond to CloudFormation unless Defer is returned.

Async responses

Your Handler method can return Defer to signal asynchronous processing.

To later respond, you need a copy of the original event object. This will be passed to the Responder class, e.g:

with Responder(event) as responder:
    responder.success(physical_resource_id="123", data={"Meta": "Data"})
    # or
    responder.failure(physical_resource_id="456", reason="Something went wrong")

Using with, your resource will always respond to CloudFormation even on exception - ensuring your stack doesn’t stall and eventually timeout.

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Files for custom_resource, version 0.1.9
Filename, size File type Python version Upload date Hashes
Filename, size custom_resource-0.1.9.tar.gz (5.2 kB) File type Source Python version None Upload date Hashes View

Supported by

Pingdom Pingdom Monitoring Google Google Object Storage and Download Analytics Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN DigiCert DigiCert EV certificate StatusPage StatusPage Status page