Stateful Services and Distributed Systems Patterns Questions

This topic covers design and implementation patterns for building stateful distributed systems in production. Candidates should be able to discuss data partitioning and sharding, replication and leader election strategies, consistency models and their trade offs, consensus algorithms, idempotent processing and at least once versus exactly once semantics, event sourcing and materialized views, stream processing with state and checkpointing, caching and eviction policies, distributed transactions or saga patterns, and techniques for scaling state under high concurrency. Strong answers also cover monitoring, observability, testing strategies for correctness under failure, and operational practices for safe rollouts and recovery.