Serverless Functions

Serverless functions (Function-as-a-Service) allow deploying individual functions that run in response to events -- HTTP requests, queue messages, database changes, scheduled timers -- without provisioning or managing servers. The cloud provider handles all infrastructure, scaling instances from zero to thousands automatically based on demand, and billing is based on actual execution time (measured in milliseconds) and memory allocation rather than reserved capacity.

AWS Lambda, Google Cloud Functions, Azure Functions, Cloudflare Workers, and Vercel Functions are the major platforms. Each function receives an event payload and a context object, executes its logic, and returns a response. Functions should be stateless and idempotent, storing any persistent state in external services (databases, S3, Redis). Cold starts -- the latency penalty when a new execution environment is initialized -- are a key concern, mitigated by keeping deployment packages small, using provisioned concurrency for latency-sensitive endpoints, and choosing runtimes with fast startup (Node.js, Python, Go over Java/C#).

Serverless functions excel for event-driven workloads (webhooks, image processing, ETL pipelines), APIs with variable traffic (scaling to zero during idle periods), and extending existing applications with isolated microservices. They are less suited for long-running tasks (most platforms cap execution at 15 minutes), workloads requiring persistent connections (WebSockets, database connection pooling requires RDS Proxy or similar), and latency-sensitive endpoints where cold starts are unacceptable. The Serverless Framework, SST, and SAM provide tooling for managing serverless applications across environments.