CodeSignal Technical Assessment System Design and Architecture 2

Question 1

A payment service must guarantee that a transaction is processed exactly once even if retries occur. Which pattern best addresses this?

Accepted Answer

Idempotency keys stored server-side

Answer

Idempotency keys allow clients to retry safely because the server deduplicates requests by key and returns the original result.

Question 2

You need to fan out a single event to 10,000 subscribers with low latency. Which messaging topology is most appropriate?

Accepted Answer

Pub/sub topic with push delivery

Answer

Pub/sub topics push messages to all subscribers simultaneously, making fan-out efficient without sender knowledge of each consumer.

Question 3

Which consistency model allows reads to see stale data but guarantees eventual convergence across replicas?

Accepted Answer

Eventual consistency

Answer

Eventual consistency permits temporary staleness but guarantees all replicas will converge to the same value given no new updates.

Question 4

A microservice architecture experiences cascading failures when a downstream service is slow. Which pattern prevents this?

Accepted Answer

Circuit breaker

Answer

A circuit breaker trips after repeated failures, stopping calls to the unhealthy service and allowing it time to recover.

Question 5

You are designing a URL shortener expected to handle 10,000 writes/sec. What is the primary bottleneck to address first?

Accepted Answer

Unique ID generation at scale

Answer

At high write rates, generating collision-free short codes becomes the bottleneck; solutions include Snowflake IDs or distributed counters.

Codesignal Practice Test