backend_stack.py

from aws_cdk import (
    # Duration,
    CfnOutput,
    Duration,
    Environment,
    Stack,
    aws_dynamodb as dynamo,
    aws_timestream as timestream,
    aws_lambda as lambda_,
    aws_lambda_event_sources as lambda_event_sources,
    aws_sqs as sqs,
    aws_sns as sns,
    RemovalPolicy
)
from constructs import Construct

class BackendStack(Stack):

    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)

        time_to_live_attribute = '_expireOn'

        # [ ] 3.1.1: create DynamoDB orders table [docs](https://docs.aws.amazon.com/cdk/api/v2/python/aws_cdk.aws_dynamodb/Table.html)
        orders_table = dynamo.Table(self, 'orders',
            partition_key=dynamo.Attribute(name='customer', type=dynamo.AttributeType.STRING),
            sort_key=dynamo.Attribute(name='id', type=dynamo.AttributeType.STRING),
            billing_mode=dynamo.BillingMode.PAY_PER_REQUEST,
            stream=dynamo.StreamViewType.NEW_AND_OLD_IMAGES,
            time_to_live_attribute=time_to_live_attribute,
            removal_policy=RemovalPolicy.DESTROY
        )

        # [ ] 3.1.2: connect api to dynamodb
        CfnOutput(self, 'ordersTableName-py', 
            export_name='ordersTableName-py', 
            value= orders_table.table_name
        )

        CfnOutput(self, 'ordersTableArn-py', 
            export_name='ordersTableArn-py', 
            value= orders_table.table_arn
        )

        # [ ] 4.1.1: create processing orders queue
        orders_queue = sqs.Queue(self, 'ordersQueue', 
            visibility_timeout=Duration.seconds(60)
        )

        # [ ] 4.1.2: create user notification topic (sns)
        user_notification_topic = sns.Topic(self, 'userNotification')

        # [ ] 4.2.1: create a lambda to handle dynamodb stream
        dynamo_lambda = lambda_.Function(self, 'dynamoHandler',
            runtime=lambda_.Runtime.NODEJS_16_X,
            code=lambda_.Code.from_asset('../functions/dynamo-handler'),
            handler='index.handler'
        )
        dynamo_lambda.add_environment('QUEUE', orders_queue.queue_url)
        dynamo_lambda.add_environment('TS_DB', '')
        dynamo_lambda.add_environment('TS_TABLE', '')
        CfnOutput(self, 'dynamoLambda-py', 
            value= dynamo_lambda.function_name
        )

        # [ ] 4.2.2: create a lambda to handle sqs messages
        sqs_lambda = lambda_.Function(self, 'sqsHandler',
            runtime=lambda_.Runtime.NODEJS_16_X,
            code=lambda_.Code.from_asset('../functions/sqs-handler'),
            handler='index.handler'
        )
        sqs_lambda.add_environment('QUEUE', orders_queue.queue_url)
        CfnOutput(self, 'sqsLambda-py', 
            export_name='sqsLambda-py', 
            value= sqs_lambda.function_name
        )


        # [ ] 4.3.1: set lambda 4.2.1 as handler for dynamodb table updates
        orders_table.grant_stream_read(dynamo_lambda)
        dynamo_lambda.add_event_source(lambda_event_sources.DynamoEventSource(orders_table,
            starting_position=lambda_.StartingPosition.TRIM_HORIZON,
            batch_size=10
        ))

        # [ ] 4.3.2: set lambda 4.2.2 as handler for sqs queue messages
        orders_queue.grant_send_messages(sqs_lambda)
        sqs_lambda.add_event_source(
            lambda_event_sources.SqsEventSource(orders_queue, batch_size= 2)
        )