What is Serverless Functions?
Individual functions that run on-demand in the cloud without you managing servers. Each function handles a specific task, scales automatically, and you only pay for the execution time used.
In plain English
Serverless functions are like calling a taxi versus owning a car. With a car (server), you pay for parking, insurance, and maintenance whether you're driving or not. With a taxi (serverless), you pay only for each ride. It's cheaper for occasional trips but can add up for constant use.
How it works
Serverless functions are single-purpose code blocks deployed to a cloud provider (Vercel Functions, AWS Lambda, Cloudflare Workers). When a request triggers the function, the cloud provider allocates resources, runs the code, and deallocates them. Functions start up on demand (cold start), process the request, and shut down. They're stateless — each invocation is independent.
Why it matters for AI-built apps
Serverless is the default deployment model for modern Next.js apps on Vercel — each API route becomes a serverless function. This means zero infrastructure management and automatic scaling. However, AI-generated code may not account for serverless constraints: cold starts, execution time limits, stateless execution, and connection limits to databases.
Common issues
Cold start latency (first request is slow), execution time limits (Vercel: 10s hobby, 60s pro), database connection exhaustion (each function opens a new connection), state not persisting between invocations, large function sizes causing slow cold starts, and not understanding the cost model (many short invocations can be expensive).
Best practices
Keep functions small and focused. Use connection pooling for databases (PgBouncer, Supabase pooler). Minimize dependencies to reduce cold start time. Set up proper error handling and timeouts. Use edge functions for latency-sensitive operations. Monitor function execution times and costs. Consider a persistent server for long-running tasks or WebSocket connections that serverless can't handle.
Frequently asked questions
Are Next.js API routes serverless functions?
On Vercel, yes — each API route becomes a serverless function by default. This means each route has independent scaling, cold starts, and execution limits. On self-hosted Next.js, API routes run as part of a long-running Node.js process. Understanding this distinction is important for database connections, file system access, and in-memory caching.
Why are my API routes slow on the first request?
That's a cold start — the serverless function needs to initialize on the first request after being idle. Cold starts typically add 200ms–2s of latency. To reduce them: minimize dependencies (fewer node_modules to load), use smaller function sizes, consider edge functions for latency-critical endpoints, and keep functions warm with scheduled pings if needed.
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