CloudFormation Custom Resources Overview

• Purpose: Custom resources are used to define resources not natively supported by CloudFormation or to implement custom provisioning logic.
• Use Cases:
  • Managing on-premises resources.
  • Integrating third-party resources.
  • Running custom scripts during stack lifecycle events (create, update, delete) via Lambda functions.

Common Exam Point

• Emptying S3 Bucket: A popular exam topic is using a Lambda function to empty an S3 bucket before deletion, as CloudFormation cannot delete a non-empty S3 bucket.

Defining a Custom Resource

• Resource Type: Custom resources are defined with the type Custom::MyCustomResourceTypeName.
• Backed By: The custom resource can be backed by a Lambda function (most common) or an SNS topic.
• Location: The backing Lambda function or SNS topic must be in the same region as the custom resource.

Lambda Custom Resource

• Properties:
  • ServiceToken: The ARN of the Lambda function or SNS topic.
  • Input Data Parameters: Allows passing input values to the Lambda function.

Example Use Case

• Deleting S3 Bucket Contents:
  • Problem: CloudFormation cannot delete a non-empty S3 bucket.
  • Solution: Use a custom resource to delete all objects in the bucket first.
  • Process:
    • When the custom resource is deleted, it triggers a Lambda function.
    • The Lambda function runs API calls to empty the S3 bucket.
    • Once the bucket is empty, CloudFormation can proceed to delete it.

Diagram Explanation

• The diagram provided in the training likely illustrates the flow of events when a CloudFormation stack is deleted, showing how the custom resource interacts with the Lambda function to empty the S3 bucket before the bucket is deleted by CloudFormation.

Conclusion

• Custom resources in CloudFormation are powerful tools for extending its capabilities and integrating external logic and resources into your infrastructure management.

Next Steps

• Continue to the next lecture for more in-depth knowledge and practical examples of AWS CloudFormation.