Topic 16. The actor model and the Microsoft Orleans framework; the CAP theorem and fault tolerance of distributed systems

Goal: become familiar with the actor model, Orleans virtual actors, the CAP theorem, consistency models, and methods of ensuring fault tolerance in distributed systems; learn to create Orleans grains, silos, and clients on .NET 10, store grain state in Redis, and use timers, reminders, and streams; master building a cluster of several silos, verifying recovery after a failure, and client-side retry and circuit breaker strategies.

Lecture contents

1. The actor model and the Orleans project — The actor model · Orleans virtual actors · An Orleans project on .NET 10
2. Grain execution and state — The execution model: turns and reentrancy · Grain state and persistence
3. Timers, streams, and the Orleans cluster — Timers, reminders, streams, and monitoring · The Orleans cluster and silo failures
4. CAP, consistency, and fault tolerance — The CAP theorem and PACELC · Consistency models and quorums · Consensus: Paxos and Raft · Fault tolerance of distributed systems
5. Case studies and common mistakes — Examples of actor-based architectures · Program examples · Common mistakes

Practice and review

• Practice — 3 worked examples with complete code and output
• Tasks — 30 variants, each with tasks at three difficulty levels
• Summary — conclusions, self-check questions, and useful links