Lambda with DynamoDB Streams in AWS - Step-by-Step Execution

Process Flow - Lambda with DynamoDB Streams

DynamoDB Table

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Data Change: Insert/Update/Delete

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DynamoDB Stream Records

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Lambda Triggered

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Lambda Processes Records

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Lambda Executes Business Logic

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Optional: Write to Other Services

When data changes in DynamoDB, the change is sent as a stream record. Lambda listens to these records and runs code to process them.

Execution Sample

AWS

1. Insert item into DynamoDB
2. Stream captures change
3. Lambda triggered with stream event
4. Lambda reads event records
5. Lambda processes each record

This sequence shows how a DynamoDB data change triggers a Lambda function via streams.

Process Table

Step	Event	Stream Record	Lambda Action	Result
1	Insert item into DynamoDB	New image with item data	No action yet	Stream captures change
2	Stream record created	Record with eventName: INSERT	Lambda triggered	Lambda receives event with records
3	Lambda starts processing	Reads record data	Parses new image	Extracts item details
4	Lambda processes record	EventName is INSERT	Executes insert logic	Processes new item
5	Lambda completes	No more records	Returns success	Changes processed
6	No new stream records	No event	Lambda idle	Waiting for next trigger

💡 No more stream records to process, Lambda finishes execution.

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
streamRecords	[]	[record1]	[record1]	[record1]	[]
lambdaEvent	null	{records:[record1]}	{records:[record1]}	{records:[record1]}	null
processedItems	0	0	1	1	1

Key Moments - 3 Insights

Why does Lambda get triggered multiple times?

Lambda triggers each time new stream records appear, as shown in execution_table rows 2 and 6 where Lambda waits for new events.

What happens if multiple records arrive at once?

Lambda receives all records in one event and processes them one by one, as seen in execution_table row 3 where Lambda reads all records.

Does Lambda modify the DynamoDB table directly?

No, Lambda processes stream data and can write elsewhere, but the original DynamoDB change already happened before Lambda runs, as shown in step 1.

Visual Quiz - 3 Questions

Look at the execution_table, what triggers the Lambda function?

A A direct API call to Lambda

B A new record appearing in the DynamoDB stream

C A scheduled timer event

D Manual invocation by user

💡 Hint

See execution_table row 2 where Lambda is triggered by a stream record.

At which step does Lambda parse the new item data from the stream?

A Step 3

B Step 5

C Step 1

D Step 6

💡 Hint

Check execution_table row 3 where Lambda reads and parses the record.

If no new stream records arrive, what is Lambda's state?

A Lambda processes old records repeatedly

B Lambda triggers continuously without data

C Lambda remains idle waiting for new events

D Lambda deletes the DynamoDB table

💡 Hint

See execution_table row 6 where Lambda is idle waiting for new triggers.

Concept Snapshot

DynamoDB Streams capture table changes.
Lambda triggers on new stream records.
Lambda processes each record's data.
Lambda runs code after data change.
Useful for reacting to DB updates automatically.

Full Transcript

When you add, update, or delete data in a DynamoDB table, the change is recorded in a stream. This stream sends records about the change. AWS Lambda listens to these stream records and runs your code automatically. The Lambda function reads each record, understands what changed, and can do tasks like updating other systems or sending notifications. Lambda only runs when there are new stream records, so it waits quietly otherwise. This setup helps you react quickly and automatically to database changes without manual steps.