What Are Serverless Functions?
Serverless functions – often called Function‑as‑a‑Service (FaaS) – let you run discrete units of code without provisioning or managing servers. Instead of launching a VM or container, you simply upload your function, declare an event trigger, and the cloud provider takes care of scaling, maintenance, and billing.
Why Use Serverless?
- Cost efficiency: Pay only for actual invocations, not idle compute.
- Zero ops: No server updates, patches, or capacity planning.
- Instant scaling: Handles 1 request per second or 100,000+ per minute with no code change.
- Rapid iteration: Deploy new features in seconds, test locally, roll back instantly.
- Event‑driven: Perfect for background jobs, APIs, scheduled tasks, IoT data pipelines.
Popular Providers
- AWS Lambda
- First‑mover with tight integration to the AWS ecosystem.
- Azure Functions
- Seamless with Microsoft stack, C# support.
- Google Cloud Functions
- Great for event‑driven workloads, built on Cloud Run.
- Vercel Edge Functions
- Ultra‑fast, globally distributed, perfect for front‑end hooks.
A Minimal Example (Node.js)
Below is a simple HTTP handler that returns the current UTC time.
// index.js
exports.handler = async (event, context) => {
const now = new Date().toISOString();
return {
statusCode: 200,
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({ currentTime: now })
};
};
Upload index.js to your provider, set the handler to index.handler, and bind it to an HTTP trigger.
Cold Starts – The Achilles’ Heel
When a function hasn't run in a while, the platform must boot a new container – that's a cold start. It can add 200‑500 ms of latency. Mitigation tactics include:
- Keep the function warm by scheduling a tiny “heartbeat” invocation.
- Use provisioned concurrency (if available).
- Minimize package size – tree‑shake dependencies.
- Prefer runtime languages with fast startup (e.g., Go, Node 14+).
When Not to Use Serverless
- Long‑running, stateful workloads (e.g., 10‑hour data pipelines).
- Applications requiring low‑latency, deterministic performance.
- Environments with strict vendor lock‑in constraints.