CRUDL Handlers

CRUDL Handlers

How a Handler Implements Create, Read, Update, Delete and List

Create, update and delete handlers must answer within 60 seconds with a progress event: IN_PROGRESS, SUCCESS or FAILED. A slow operation returns IN_PROGRESS with a callback context, and CloudFormation 24 calls again with it until success, failure or the schema's timeoutInMinutes (default 120; 720 for tables). Read returns the live model or NotFound; list returns every identifier. LocalStack 63,725 's providers follow the same contract in Python; this is 4.13.1's table delete handler, from services/dynamodb/resource_providers/aws_dynamodb_table.py in the container:

LocalStack 4.13.1's delete handler for a DynamoDB table (excerpt, calls condensed)YAML

        model = request.desired_state
        if not request.custom_context.get(REPEATED_INVOCATION):
            request.custom_context[REPEATED_INVOCATION] = True
            request.aws_client_factory.dynamodb.delete_table(TableName=model["TableName"])
            return ProgressEvent(status=OperationStatus.IN_PROGRESS, ...)
        try:
            table_state = request.aws_client_factory.dynamodb.describe_table(
                TableName=model["TableName"]
            )
            match table_state["Table"]["TableStatus"]:
                case "DELETING":
                    return ProgressEvent(status=OperationStatus.IN_PROGRESS, ...)
                case invalid_state:
                    return ProgressEvent(status=OperationStatus.FAILED, ...)
        except request.aws_client_factory.dynamodb.exceptions.TableNotFoundException:
            return ProgressEvent(status=OperationStatus.SUCCESS, resource_model={})

The first call starts the deletion and marks the context; later calls only poll, and "not found" means success. Providers you write with the CloudFormation CLI 338 (github.com/aws-cloudformation/cloudformation-cli (https://github.com/aws-cloudformation/cloudformation-cli 338 ), pip 21,050 install cloudformation-cli plus a Java, Go, Python or TypeScript plugin) work the same way, and cfn test runs the contract tests they must pass.

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