Questions 46 to 48

Question 46

You are a solutions architect at Digital Cloud Training. One of your clients runs an application that writes data to a DynamoDB table. The client has asked you how they can implement a function that runs code in response to item level changes that take place in the DynamoDB table. What would you suggest to the client?

1. Enable server access logging, and create an event source mapping between AWS Lambda and the S3 bucket to which the logs are written.
2. Enable DynamoDB Streams, and create an event source mapping between AWS Lambda and the relevant stream.
3. Create a local secondary index that records item level changes, and write some custom code that responds to updates to the index.
4. Use Kinesis Data Streams, and configure DynamoDB as a producer.

Correct Answer: 2

Explanation: DynamoDB Streams help you keep or provide a list of item level changes that have taken place in the last 24 hours. Amazon DynamoDB is integrated with AWS Lambda so that you can create triggers, which are pieces of code that automatically respond to events in DynamoDB Streams.

If you enable DynamoDB Streams on a table, you can associate the stream ARN with a Lambda function that you write. Immediately after an item in the table is modified, a new record appears in the table’s stream. AWS Lambda polls the stream and invokes your Lambda function synchronously when it detects new stream records.

An event source mapping identifies a poll-based event source for a Lambda function. It can be either an Amazon Kinesis or DynamoDB stream. Event sources maintain the mapping configuration except for stream-based services (e.g., DynamoDB, Kinesis), for which the configuration is made on the Lambda side, and Lambda performs the polling.

INCORRECT: “Enable server access logging, and create an event source mapping between AWS Lambda and the S3 bucket to which the logs are written.” is incorrect. The question asks for a solution that runs code in response to changes in a DynamoDB table, not an S3 bucket.

CORRECT: “Enable DynamoDB Streams, and create an event source mapping between AWS Lambda and the relevant stream.” is the correct answer.

INCORRECT: “Create a local secondary index that records item level changes, and write some custom code that responds to updates to the index.” is incorrect. A local secondary index maintains an alternate sort key for a given partition key value; it does not record item level changes.

INCORRECT: “Use Kinesis Data Streams, and configure DynamoDB as a producer.” is incorrect. You cannot configure DynamoDB as a Kinesis Data Streams producer.

References:

https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Streams.Lambda.html