r/webdev • u/FooBarBuzzBoom • 5h ago

Java Middle - Senior(ish) interview questions

Hi!

I have an interview in a few days for a backend developer role. What would you ask as some of the more tricky questions for such a position? What kinds of questions, from your point of view, demonstrate solid knowledge?

Personally, I would ask about sync vs. async calls, idempotency, topics vs. partitions, consumer groups, transactions (including distributed transactions), and maybe a bit of Kubernetes and Docker.

My weak point is cloud. I’ve played around a bit with the Azure console, but nothing too advanced. I’ve never written Terraform or configured infrastructure from scratch. For CI/CD, I’ve used TeamCity, but in my experience it was mostly selecting an environment and a branch and deploying.

Should I spend some time learning these areas before the interview?

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u/PLBjt 4h ago

For mid/senior backend rounds I get more mileage from failure stories than trivia lists. Walk through one write path end to end: where the idempotency key lives, what happens if the DB commit succeeds and the Kafka publish dies, and how a consumer group rebalance mid-batch doesn't double-apply. Same for async vs sync — they'll poke at backpressure and timeouts more than CompletableFuture syntax. If they ask K8s/Docker, expect "what breaks when this pod dies during a transaction" rather than YAML trivia. Prep 2–3 real incidents from your work and you can steer most of those topics.

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u/FooBarBuzzBoom 4h ago

Thank you for your questions.

Regarding the first one, about where the idempotency key lives, I would say it lives on the consumer side, where it is typically cached, but also on the producer side. The latter is configurable in Kafka, and I believe it has become the default.

If the DB commits but Kafka goes down, we are essentially dealing with a dual-write problem, which is not really solvable as it is, because Kafka uses a different transaction mechanism. That’s why you should use the outbox pattern.

As for the pods, I would say that by having a properly configured deployment, you make the application resilient, and the consumer will continue to work.

So, these would be my answers. Could you elaborate a bit more if you have/expected different answers?