Distributed Systems

Synchronous and asynchronous service communication, RPC versus resource-oriented HTTP APIs, API compatibility, and message encoding choices.

How state placement changes routing, scalability, recovery, and storage dependencies in distributed services.

Deployment strategies for multi-instance services: downtime, blue-green, rolling, canary rollout, A/B testing, and practical rollback mechanisms.

Failure detection and common resilience behaviors including failover, fail-fast, fail-safe, fail-silent, failback, hedged/forked calls, and broadcast calls.

How distributed nodes exchange cluster metadata and the trade-offs between centralized coordination and peer-to-peer dissemination.

Why transactions become harder across services and data stores, and how 2PC, TCC, Saga, reliable messaging, reconciliation, and best-effort notification address different consistency requirements.

How two-phase commit coordinates atomic commit across transactional resources, and why blocking, coordinator failure, and long-held resources are its main costs.

Application-level distributed transactions using Try, Confirm, and Cancel operations, including reservations, compensation, retries, idempotency, and business-code cost.

How a durable business change and a durable outgoing message are coupled so downstream services can converge through retries and idempotent consumption.

A notification pattern for external or loosely coupled systems using bounded retries, durable result lookup, and reconciliation instead of atomic cross-system commit.