Serverless Architecture for Web Applications

Serverless: Running Code Without Managing Servers

Serverless computing is a way of building applications where you don't have to think about servers at all. You write your code, upload it to a cloud provider, and they handle everything else — scaling, availability, security patches. You pay only for the compute time your code actually uses, not for idle server capacity.

Functions as a Service

The most common form of serverless is Functions as a Service (FaaS). AWS Lambda, Cloudflare Workers, Vercel Functions, and similar services let you deploy individual functions that respond to events. An event might be an HTTP request, a file being uploaded, a message appearing in a queue, or a scheduled timer. The function runs, does its work, and shuts down.

This model is incredibly scalable. If one request comes in, one function runs. If a million requests come in, a million functions run in parallel. You don't need to provision capacity or worry about traffic spikes — the cloud provider handles it automatically.

The Cold Start Problem

The main downside of serverless is cold starts. When a function hasn't been used for a while, the provider needs to load your code into memory and start the runtime before it can handle the request. This adds a delay of several hundred milliseconds to the first request. For user-facing applications, this can be noticeable.

There are ways to mitigate cold starts. You can keep functions warm by sending periodic requests. You can use provisioned concurrency to keep a minimum number of instances ready. And you can choose runtimes that start faster — Node.js and Python start faster than Java or .NET. Some providers, like Cloudflare Workers, have virtually eliminated cold starts by using a different architecture.

When to Use Serverless

Serverless is great for many use cases. APIs with variable traffic patterns benefit from automatic scaling. Background tasks like image processing, video transcoding, and data transformation are perfect for serverless. Scheduled tasks like sending daily reports or cleaning up old data are simple to implement. And webhooks — where you need to respond to events from external services — are a natural fit.

Serverless is less suitable for long-running processes (functions typically have a timeout limit of 15 minutes), applications with predictable high traffic (a dedicated server might be cheaper), and workloads that require specialized hardware like GPUs.

Building a Serverless Application

A typical serverless application uses multiple services together. An API Gateway receives HTTP requests and routes them to Lambda functions. A serverless database like DynamoDB or Aurora Serverless stores data. A CDN serves static files. Authentication is handled by a service like Cognito or Auth0. And file storage uses S3 or similar object storage.

Frameworks like the Serverless Framework and SST (Serverless Stack) make it easier to define and deploy serverless applications. They provide local development environments, handle the configuration of cloud resources, and make it easy to manage multiple environments.