Ephemeral Storage

Ephemeral Storage Overview

At its core, ephemeral storage 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 ephemeral storage pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

// Initialise clients ONCE outside the handler (runs during cold start)
import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
const client = new DynamoDBClient({});

export const handler = async (event) => {
  // Warm invocations reuse the client above -> faster, cheaper
  return { ok: true };
};

Moving client creation to module scope avoids re-initialising connections on every warm invocation.

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

AWS Lambda Cheatsheet

Handy reference for working with ephemeral storage in AWS Lambda and Node.js.

How Ephemeral Storage Works in AWS Lambda

Ephemeral Storage 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.

Moving client creation to module scope avoids re-initialising connections on every warm invocation.

• 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 Ephemeral Storage

On real projects, ephemeral storage 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

• Copying ephemeral storage snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up ephemeral storage.
• Leaving ephemeral storage untested, so regressions slip into production.
• Over-engineering ephemeral storage before you actually need the extra flexibility.

Key Takeaways

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