Google DevOps System Design & Architecture interview questions

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.

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 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.

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.

Type-ahead is a latency budget wearing a search costume: keystrokes arrive every 200 milliseconds, so anything slower feels broken. Prefix indexes, freshness tiers, and typo tolerance are the scored parts.

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.

Reciting both acronyms is the median answer. Expert level chooses by connectivity assumptions and undo semantics, then defends CRDT metadata growth with numbers.

Comparing the canary against last week is how a Tuesday afternoon looks like a regression. Compare it against a baseline running the same traffic at the same moment, and decide with a threshold somebody can defend.

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.

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 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.

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.

The vocabulary question hiding real depth: which primitive replaces ORDER BY, why sharding by player is wrong, and what a 45,000 updates-per-second storm actually costs.

Two contracts in one system: an OTP with a 30-second promise and a sale announcement reaching fifty million phones without burning providers. Priority lanes and double-layer dedup decide the grade.

Flags sit on the request path of everything, so a slow flag service is a site-wide outage waiting to happen. Local snapshots, propagation numbers and audit trails are where this design is decided, because they determine what happens when the flag service itself is unavailable.

Sharding buys write headroom and bills you in joins, foreign keys, and every future migration. The key choice is a query-pattern bet; the resharding choreography separates operators from diagram artists.