React when a record changes — DynamoDB Streams and Lambda

Your goal

Write a table record and read its change from DynamoDB Streams.

Why this matters

A change stream lets another part of an app notice a new record. You will enable new-image records, write a message, and retrieve its actual change record from the stream.

Words you will use

A stream is a sequence of changes. A stream record describes one item change. An image is a copy of the item before or after that change.

How to proceed

Start a fresh emulator, read each numbered step, and enter the practice settings shown. Run the action, inspect its API receipt, then continue. Finish lab checks the emulator state again before saving your progress.

1. Enable a change stream on a table

Create a DynamoDB table with NEW_IMAGE stream records. A new image contains the record after a change. This lets a consumer react without repeatedly scanning the whole table.

2. Write a recognizable record

Save practice-1 with your message. This creates a change for the stream to describe. You will look for the same message in the next API result.

Practice message: Type a short message that you can recognize in the API result. Suggested practice value: Hello from my lab.

3. Read the change record

Describe the stream, request an iterator from the start of its shard, and read its records. Find your message under NewImage. This is an actual table-to-stream check in the emulator.

Practice, then check your understanding

Perform the actions yourself and inspect the returned state. Errors keep your settings so you can retry. Starting another lab clears the previous live environment. Earned XP is kept, and signed-in achievements sync to your account. Replay does not award duplicate XP.

Read the official AWS documentation for service behavior and production details.