DynamoDB Streams

DynamoDB Streams Overview

At its core, dynamodb streams is about doing one thing well inside your AWS Lambda project. Once you understand the pattern, you can apply it consistently across features and teams.

Good dynamodb streams pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient, GetCommand, PutCommand } from '@aws-sdk/lib-dynamodb';

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const handler = async (event) => {
  await docClient.send(new PutCommand({
    TableName: process.env.TABLE_NAME,
    Item: { id: event.id, createdAt: Date.now() },
  }));

  const { Item } = await docClient.send(new GetCommand({
    TableName: process.env.TABLE_NAME,
    Key: { id: event.id },
  }));

  return Item;
};

The DynamoDB Document Client is created outside the handler so it is reused across warm invocations.

DynamoDB Streams Example

// handler.mjs
export const handler = async (event, context) => {
  // 1. read input from the event
  // 2. do the work
  // 3. return a response (or throw on error)
};

• Start from a minimal DynamoDB Streams example and grow it only as needed.
• Keep configuration explicit so DynamoDB Streams behaves the same in every environment.
• Name things clearly so teammates understand your DynamoDB Streams at a glance.
• Add tests around DynamoDB Streams early to lock in expected behaviour.

AWS Lambda Cheatsheet

Handy reference for working with dynamodb streams in AWS Lambda and Node.js.

How DynamoDB Streams Works in AWS Lambda

DynamoDB Streams runs inside the managed Lambda execution environment. AWS provisions a micro-VM, loads your Node.js code, runs any module-scope initialisation once, and then invokes your handler for each event.

The DynamoDB Document Client is created outside the handler so it is reused across warm invocations.

• Handlers should be small and do one job well.
• Initialise SDK clients and config outside the handler to reuse them on warm starts.
• Return quickly and let event sources handle retries where possible.
• Emit structured logs so CloudWatch and X-Ray can correlate activity.

Practical Guidance for DynamoDB Streams

On real projects, dynamodb streams works best when it is observable, secure, and cheap to run. Grant least-privilege IAM, validate every input, and keep the deployment package small.

Common Mistakes

• Skipping error handling and edge cases when wiring up dynamodb streams.
• Leaving dynamodb streams untested, so regressions slip into production.
• Over-engineering dynamodb streams before you actually need the extra flexibility.
• Ignoring documentation, which makes dynamodb streams hard for the next developer to change.

Key Takeaways

• DynamoDB Streams is a core part of working effectively with AWS Lambda.
• Start small and keep dynamodb streams focused on a single responsibility.
• Apply consistent patterns so dynamodb streams scales across your project.
• Test and document dynamodb streams to keep it maintainable over time.