Apple Backend Engineer Interview Questions

I would start by checking the query plan, indexes, and whether the query is scanning far more rows than it needs to. If the same data is being read repeatedly, I would also consider caching or precomputed results. The reason I start with measurement is that guesswork usually misses the real bottleneck. I would then look at schema design, access patterns, and whether the query can be rewritten more simply. If needed, I would also think about read replicas or denormalization depending on the workload.

I would separate event intake from delivery so the system can fan out notifications without blocking the main request path. My design would likely use a queue for buffering, a routing layer to decide which users and channels to notify, and workers for email, push, or in-app delivery. The reason I choose asynchronous delivery is that notification traffic can spike and individual providers may be slow or unreliable. I would also discuss retries, deduplication, user preferences, and dead-letter queues. If the interviewer asks for more detail, I would mention template management and delivery metrics.

I would use a mix of unit tests, integration tests, and a smaller number of end-to-end tests. Unit tests should cover business logic, integration tests should verify how components talk to databases or external services, and end-to-end tests should protect the main user flows. The reason I use multiple layers is that no single test type catches everything. I would also mention contract tests if services depend on each other through APIs. In an interview, I would emphasize that tests should be fast enough to run regularly and useful enough to catch real regressions.

I would say the right choice depends on team size, deployment complexity, and the degree of independent scaling the system needs. A monolith is often easier to build, test, and deploy early on, while microservices can help when different parts of the system need independent scaling or separate ownership. The reason I do not pick one blindly is that microservices also add operational overhead and distributed failure modes. I would usually favor the simplest architecture that meets the current needs. If the interviewer wants more depth, I would talk about service boundaries, data ownership, and communication costs.

I would start by following one request through logs, metrics, and traces so I can see where the behavior changes. That helps me determine whether the bug is in the API layer, business logic, database call, or downstream service. The reason I like end-to-end tracing is that backend bugs often hide in the gaps between systems. Once I isolate the failing hop, I can reproduce the issue more easily and confirm the fix with the same trace path. I would also mention correlation IDs because they make this kind of debugging much easier.