Apple Backend Engineer Interview Questions

I would start by deciding whether the service should use sessions, JWTs, or another token-based method. Then I would make sure login, token issuance, token refresh, and logout are all handled securely. The reason I choose a structured flow is that authentication mistakes often come from unclear token lifetimes or weak session handling. I would also discuss secure storage, transport encryption, and how to revoke access if a token is compromised. If the interviewer wants more depth, I would compare server-side sessions with stateless tokens.

I would keep backward compatibility as long as possible and introduce breaking changes in a controlled way. A common path is to support both versions in parallel, add a new versioned endpoint or header, and migrate clients gradually. The reason I choose this approach is that backend systems often have long-lived consumers that cannot all update at once. I would also mention deprecation notices, telemetry on old versions, and a plan for eventual cleanup. If the interviewer wants more detail, I would discuss whether versioning belongs in the URI, header, or request schema.

I would compare the new deployment against the previous one and check whether the failures are limited to one endpoint or one dependency. Then I would look at logs, error rates, and recent code changes to isolate the regression. The reason I start there is that deployment-related issues are often caused by one small change in behavior rather than a broad system failure. If the issue is severe, I would consider rollback or feature flag disablement while I keep investigating. I would also think about whether the failure is tied to a data migration or an external service change.

I would store jobs durably, let workers claim them, and make retry behavior explicit with attempt counts and backoff. If a job fails temporarily, it should be retried after a delay, but if it fails too many times it should move to a dead-letter queue. The reason I choose this approach is that retries are necessary, but uncontrolled retries can create duplicate work or overload dependencies. I would also think about visibility timeouts, idempotency, and worker crashes. If the interviewer asks, I would mention how to keep the queue from growing without bound.

I would first inspect the bottleneck instead of assuming the answer is more hardware. The main things I would check are database pressure, cache hit rate, connection pools, thread contention, and whether the service can scale horizontally. The reason I start there is that most load problems come from one constrained component. I would also consider load shedding and graceful degradation so the system remains partially usable. If the interviewer wants a concrete sequence, I would say I would measure, isolate, and then optimize the hottest path.