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Cloudmedium

Health checks: what are they and why do load balancers need them?

Tags
#health-check#load-balancer#availability
Back to categoryPractice quiz

Answer

A health check tests if an instance is ready to serve traffic. Load balancers use it to remove unhealthy instances from rotation, improving availability and reducing user-facing errors.

Advanced answer

Deep dive

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

  • Context (tags): health-check, load-balancer, availability
  • 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

A tiny example (an explanation template):

// Example: discuss trade-offs for "health-checks:-what-are-they-and-why-do-load-bal"
function explain() {
  // Start from the core idea:
  // A health check tests if an instance is ready to serve traffic. Load balancers use it to re
}

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?

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