Stateless vs stateful service: what is the difference and why does it matter?

Deep dive

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

• Context (tags): architecture, stateless, stateful, scaling
• Scaling: what scales horizontally vs vertically, where bottlenecks appear.
• Reliability: retries/circuit breakers/idempotency, observability (logs/metrics/traces).
• Evolution: keep changes cheap (boundaries, contracts, tests).
• 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

A tiny example (an explanation template):

// Example: discuss trade-offs for "stateless-vs-stateful-service:-what-is-the-diffe"
function explain() {
  // Start from the core idea:
  // A stateless service keeps request state outside the instance (e.g., in a DB/Redis), so any
}

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?