Meta DevOps System Design & Architecture interview questions

The Google-style NALSD round in miniature. The boxes are easy; what is being scored is whether the numbers fall out of Little's law before you draw them.

The app server that proxies uploads through itself is the design that fails this question. Direct-to-storage, validate after arrival, and make CDN invalidation almost never necessary.

Dual-writing from application code is the answer that fails quietly six months in. Change data capture, per-entity ordering, and a reindex you could run on a Tuesday are what interviewers score.

Drawing an agent that polls a server is the easy third. The interview is about partial applies, fleet-versus-world state, and why rollback must be a pointer flip, never a reverse edit.

Erasure is a distributed transaction across systems that were never designed to participate in one, and backups make a literal delete impossible. The design that works is a deletion ledger plus crypto-shredding, not a fan-out of delete statements.

The Indian e-commerce interview question, and autoscaling is the wrong first answer. A 10x spike arriving in seconds outruns any scaling loop, so the design has to absorb rather than scale.

The design round where the honest answer is mostly about data. Stateless traffic across regions is straightforward; the database is where active-active is either solved or pretended.

Stateless does not mean there is no state. It means the state is not in the instance, which is what lets you kill any instance at any time. Every scaling and deployment property people want depends on that one thing.

It converts a synchronous failure into a delay. That is the whole benefit and the whole cost, because the caller now gets an answer before the work has happened and somebody has to tell them when it did.

The classic napkin-math question. The number in the prompt is the question. Drawing the architecture before doing the arithmetic produces a design the physics forbids, and the arithmetic takes a minute.

The migration question, and the trap is answering with a target architecture. What is being scored is sequencing: how you get there without a rewrite and without a release freeze.

Every candidate says replication and failover. The scoring answer names the replication mode, states the resulting data loss window, and explains how the cluster avoids two primaries.

The default answer is 'horizontal' because interviews reward it. The correct answer names the constraint that makes distribution expensive and knows when one big machine is the engineering choice.

Everyone names token bucket. The scored part is the rest: drift between nodes, the 429 contract with clients, and whether your quota service should fail open or closed.

The catalog is the easy half. The scored half is stampede dynamics: one hot key expiring can multiply origin load by a thousand in a second, and there are three distinct fixes.

Cron is the most-deployed scheduler on earth and the worst-behaved at scale. The scored content is everything crontab cannot do: exactly-once firing, thundering herds, and what happens when the scheduler itself dies.

CAP is not a menu of two letters per system. The scored answer knows what the theorem claims (narrowly), what most engineers misquote, and what a split-brain costs when both halves accept writes.

Timeouts guarantee uncertainty, not failure: the first request may have succeeded after the client gave up. The idempotency key pattern is the industry answer; the scored details are storage, expiry and concurrency.

The most rehearsed design question, which is exactly why the interesting parts are the ones blog posts skip: redirect semantics, key generation under failure, and analytics kept off the hot path.

Outbound delivery looks like a queue and a loop until one subscriber hangs for sixty seconds and takes your workers with it. Isolation, retry horizons, and signatures are where the marks are.