Cloudeasy

What is a microservice?

Answer

A microservice is a small service that does one business thing and can be deployed independently. It usually owns its data and talks to other services via APIs/events, so it can scale and release separately.

const express = require('express');
const app = express();
const port = 3000;

app.get('/users', (req, res) => {
  res.json([{ id: 1, name: 'Alice' }]);
});

app.listen(port, () => {
  console.log(`Microservice listening at http://localhost:${port}`);
});

Advanced answer

Deep dive

Expanding on the short answer — what usually matters in practice:

Context (tags): microservices, architecture, distributed-systems
Lifecycle: what happens at runtime (render/build, request/response, background jobs).
Caching: where cache lives, cache keys, how to invalidate without chaos.
Security: authn/authz, secrets, attack surface (SSRF/CSRF).
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.

Examples

Here’s an additional example (building on the short answer):

const express = require('express');
const app = express();
const port = 3000;

app.get('/users', (req, res) => {
  res.json([{ id: 1, name: 'Alice' }]);
});

app.listen(port, () => {
  console.log(`Microservice listening at http://localhost:${port}`);
});

Common pitfalls

Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).
Ignoring constraints: memory, concurrency, network/disk costs.

Interview follow-ups

When would you choose an alternative and why?
What production issues show up and how do you diagnose them?
How would you test edge cases?