Event-driven architecture patterns in DynamoDB - Step-by-Step Execution

Concept Flow - Event-driven architecture patterns

Event Occurs

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Event Captured by Producer

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Event Sent to Event Bus or Stream

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Event Consumed by One or More Consumers

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Consumers Process Event and Update DynamoDB Tables

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Optional: Trigger Further Events

Events happen and are sent to a stream or bus. Consumers listen and react by updating DynamoDB or triggering more events.

Execution Sample

DynamoDB

1. Event: New Order Created
2. Producer sends event to DynamoDB Stream
3. Consumer Lambda triggered by stream
4. Lambda updates Order Status in DynamoDB
5. Lambda triggers Shipment Event

Shows how an order creation event flows through DynamoDB Streams to update tables and trigger next steps.

Execution Table

Step	Action	Event/Data	Result/Effect
1	Order Created	{orderId: 123, status: 'NEW'}	Event generated
2	Event sent to DynamoDB Stream	Order Created Event	Stream records event
3	Consumer Lambda triggered	Reads event from stream	Lambda invoked
4	Lambda updates DynamoDB	Updates order status to 'PROCESSING'	Order table updated
5	Lambda triggers Shipment Event	{orderId: 123, action: 'SHIP'}	New event created
6	Shipment Consumer triggered	Reads shipment event	Shipment process started
7	No more events	End of event chain	Execution stops

💡 No more events to process, event-driven flow ends

Variable Tracker

Variable	Start	After Step 1	After Step 4	After Step 5	Final
orderStatus	null	'NEW'	'PROCESSING'	'PROCESSING'	'PROCESSING'
eventQueue	empty	Order Created Event	Order Created Event	Shipment Event added	empty after processing

Key Moments - 3 Insights

Why does the consumer Lambda get triggered after the event is sent to the DynamoDB Stream?

Because DynamoDB Streams capture table changes as events, and the Lambda is configured to listen to these streams, triggering automatically when new events appear (see execution_table step 3).

How does the event-driven pattern help keep the system responsive?

Events allow different parts of the system to react independently and asynchronously, so updates happen as soon as events occur without waiting for other processes (see execution_table steps 4 and 5).

What happens if no consumer processes an event?

The event remains in the stream until processed or expires, but no updates happen in DynamoDB, so the system state does not change (implied by exit_note and variable_tracker).

Visual Quiz - 3 Questions

Look at the execution_table, what is the orderStatus after Step 4?

A 'PROCESSING'

B 'SHIPPED'

C 'NEW'

D null

💡 Hint

Check the variable_tracker column 'After Step 4' for orderStatus value.

At which step does the consumer Lambda get triggered?

A Step 2

B Step 3

C Step 5

D Step 6

💡 Hint

Look at execution_table step descriptions for Lambda trigger.

If the eventQueue remains empty after Step 5, what does that mean?

A Events are still waiting to be processed

B No events were created

C All events have been processed

D The system crashed

💡 Hint

Refer to variable_tracker for eventQueue final state.

Concept Snapshot

Event-driven architecture uses events to trigger actions asynchronously.
DynamoDB Streams capture changes as events.
Consumers (like Lambda) listen to streams and react.
This decouples components and improves responsiveness.
Events can trigger further events for workflows.

Full Transcript

Event-driven architecture in DynamoDB means when something changes, like a new order, that change creates an event. This event goes into a DynamoDB Stream. A consumer, such as a Lambda function, listens to this stream. When it sees the event, it runs and updates the database or triggers more events. This way, different parts of the system work independently but stay in sync by reacting to events. The execution table shows each step from order creation to shipment event. Variables like orderStatus change as events are processed. This pattern helps systems stay fast and flexible.