Services Covered

  • dynamodb DynamoDB
  • lambda Lambda

Lab description

In this lab you will create a new Lambda Function and connect it to the DynamoDB Stream. The table will contain basic data about users, defining only the existing fields. You will implement a simple trigger to keep the IsPersonalEmail and Email fields synchronized: every time a new record is created, the Lambda Function will add the computed field (IsPersonalEmail). Additionally, each time a record is updated, the two fields will keep in sync.


Learning Objectives

  • Enabling streams on DynamoDB table
  • Create a Lambda function and connect it to the DynamoDB Stream

Lab date

29-11-2021


Prerequisites

  • AWS account

Lab steps

  1. In the DynamoDB dashboard create a table. Then in the Exports and streams tab enable DynamoDB streams. Select the New and old images option to view both modified and pre-modified items

  2. Navigate to the Lambda dashboard. Create a new function with Python 3.8 as runtime. The code will check newly created items in the table and if the provided email has gmail.com, outlook.com or hotmail.com it will mark the IsPersonalEmail field in the table as true. Implement the following code:
    import json
    import boto3
    DDB = boto3.resource("dynamodb").Table("CloudAcademyLabs")
    def lambda_handler(event, context):
       records = event["Records"]
       print("Received %s records" % len(records))
       for record in records:
           print(record)
           # if new record or update
           if record["eventName"].upper() in {"INSERT", "MODIFY"}:
               # primary key
               record_id = record["dynamodb"]["Keys"]["Id"]["S"]
               # init local vars
               old_email = old_is_personal = new_email = new_is_personal = None
               # new and old images
               old_image = record["dynamodb"].get("OldImage") or {}
               new_image = record["dynamodb"].get("NewImage") or {}
               # old values (optional, only on update)
               if "Email" in old_image:
                   old_email = old_image["Email"]["S"]
               if "IsPersonalEmail" in old_image:
                   old_is_personal = old_image["IsPersonalEmail"]["BOOL"]
               # new values
               if "Email" in new_image:
                   new_email = new_image["Email"]["S"]
                   new_is_personal = is_personal_email(new_email)
               # avoid recursion on update and write only if strictly needed
               if old_email != new_email and old_is_personal != new_is_personal:
                   update_record(record_id, new_is_personal)
       print("Processed %s records" % len(records))
    def update_record(record_id, is_personal):
       print("Updating %s: IsPersonalEmail=%s" % (record_id, is_personal))
       DDB.update_item(
           Key={"Id": record_id},
           UpdateExpression="SET IsPersonalEmail = :val",
           ExpressionAttributeValues={":val": is_personal or False},
       )
    def is_personal_email(email):
       domains = {"gmail.com", "outlook.com", "hotmail.com"}
       return any(email.endswith(domain) for domain in domains)

    Change the function’s timeout, click Edit, change the value of the Timeout to 1 minute.

  3. In the Function overview section, click Add trigger. Select DynamoDB and the table created earlier. Starting position: Select Trim horizon from the dropdown menu.
  4. Back in the DynamoDB, create an item in JSON format.
    {
    "Id": {
     "S": "ID1"
    },
    "Email": {
     "S": "john@example.com"
    }
    }

    Put more items to see if the code works

Lab files

Acknowledgements

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