A Native Way to Run Web Apps on Lambda
AWS just launched Lambda Web Functions, a new way to run web apps natively on Lambda. Until now, running a web app on Lambda meant reshaping it around events, usually with an adapter layer between your framework and the Lambda runtime. With Lambda Web Functions, your code handles HTTP requests directly. It listens on a port and serves requests the same way it would on any HTTP server, so you can bring an existing Node.js app, framework and all, without Lambda-specific changes.
As AI-assisted development speeds up how quickly teams ship, developers want to build locally and deploy with a programming model they already know. That’s why we’re bringing AWS Lambda Web Functions support to LocalStack from day one. If Lambda can run your web app as it is, you should be able to build and test it locally the same way, with the AWS services it depends on running right beside it.
What’s New in AWS Lambda Web Functions
AWS Lambda Web Functions are a new type of Lambda function built for HTTP. They bring three main improvements: a familiar programming model, pricing based on active CPU usage, and low latency for end users.
Beyond removing adapter code, they address two long-standing pain points for web apps on Lambda: keeping performance steady as traffic grows, and paying for time spent waiting on other services, such as a large language model (LLM) generating a response.
Here’s how each improvement works:
- Familiar programming model: AWS Lambda Web Functions use a standard web programming model instead of an event handler. There’s no Lambda Web Adapter, wrapper, or event context to manage, and you can use frameworks you already know, such as Express or Hono. Node.js is the supported runtime today. You can stream results to clients incrementally with native HTTP streaming, and AWS manages each endpoint’s HTTPS domain and TLS certificate.
- Active CPU pricing: Billing is metered on active CPU time plus the memory your environment holds, so you’re not billed for CPU while a request waits on I/O, such as a database query or a downstream service call. Lambda runs the execution environments and scales with traffic, including down to zero when idle.
- Low latency: A single warm execution environment can serve multiple concurrent requests, which sharply reduces how often requests hit a cold start. You can also opt in to multi-region routing: deploy once, and each request is served from the region with the lowest latency for that user.
Common workloads include AI inference endpoints, server-side rendered (SSR) web apps, streaming API endpoints, microservices, and webhooks.
Testing a New Kind of Lambda App
Because your code now runs as a server with routes and ongoing request handling, test suites built around single events fall short. You need to test the whole app: which routes respond, how it works with other AWS services, and how changes affect its behavior.
A typical web app rarely runs on Lambda alone. It might sit behind CloudFront for caching and a custom domain, store assets in S3, read and write data in DynamoDB, and call other AWS services from its routes. Without a local environment, the only way to test how those pieces work together is to deploy to AWS. That means waiting for deployments, requesting access, and sharing environments with other teams.
With LocalStack, you can build and test AWS Lambda Web Functions locally, alongside the rest of your AWS stack, and then deploy to AWS when you’re ready.
At launch, LocalStack supports:
- Running locally or on Kubernetes: Deploy your Node.js app and send HTTP requests to it while it runs in LocalStack-managed Docker containers or Kubernetes pods.
- Hot reloading with Docker: Edit your application code locally and test changes without rebuilding or uploading a deployment package.
- Deploying with CloudFormation: Define web functions, revisions, and endpoints as CloudFormation resources and deploy them to LocalStack.
- Connecting to AWS services locally: Test routes that call LocalStack-emulated services such as S3 and DynamoDB.
- Testing with CloudFront: Put a LocalStack-emulated CloudFront distribution in front of your app and test requests end to end.
- Securing endpoints with IAM: Test SigV4-signed requests to IAM-authenticated endpoints, along with resource policies and cross-account invocation.
- Testing streaming and concurrency: Verify streamed responses, overlapping requests, timeouts, and configured throttling behavior.
- Managing revisions and traffic: Create revisions and test weighted traffic routing between them.
- Testing multi-region endpoints: Use per-region and multi-region endpoints locally, just as you would configure them on AWS.
- Inspecting application behavior: View application logs, plus supported request and error metrics, through LocalStack’s CloudWatch emulation.
- Persisting and sharing state: Keep your web functions across restarts with persistence, and snapshot or share your setup with Cloud Pods.
Built for Apps That Ship Fast
Developers increasingly build lightweight web apps for their teams, often with AI coding assistants. Previewing these apps is easy, but thorough testing before deployment tends to fall by the wayside.
Consider an internal dashboard built quickly with a frontend framework and a minimal API, then promoted to a customer-facing tool. With AWS Lambda Web Functions, moving it to Lambda is straightforward. Catching behavior gaps before they reach customers is the harder part.
With LocalStack, your app goes through the same local testing cycle as your other AWS workloads, so issues surface before production.
Support for AWS Lambda Web Functions isn’t just one more isolated feature. It opens up a new class of serverless web apps you can build and test locally before they reach AWS.
Keeping Pace with AWS
New cloud capabilities deliver the most value when teams can adopt them right away. That’s why we were excited to work with AWS ahead of this launch, so LocalStack would support AWS Lambda Web Functions from day one.
As AWS evolves, our commitment stays the same: to keep extending LocalStack’s coverage so you can try what’s new locally, as soon as possible.
Get Started Today
AWS Lambda Web Functions support is available now in LocalStack for AWS 2026.10.0, on every plan from Hobby and up. Check out the Lambda Web Functions documentation for more details on how to use them in LocalStack.
See it live: Join our hands-on webinar with the AWS Lambda team on October 22 at 10AM ET.
