Provisioned Concurrency

Provisioned Concurrency Overview

At its core, provisioned concurrency 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 provisioned concurrency 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.

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

AWS Lambda Cheatsheet

Handy reference for working with provisioned concurrency in AWS Lambda and Node.js.

How Provisioned Concurrency Works in AWS Lambda

Provisioned Concurrency 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 Provisioned Concurrency

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

Key Takeaways

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