Actors, Evolved.

The actor model is a novel approach to writing concurrent software. It is based on the concept of small computational units communicating through asynchronous message passing, thus allowing concurrency and scalability while negating a lot of the problems of concurrent programming.

Though the actor model got some adoption with the Erlang language and the Akka framework, it remained a rather niche approach and has not become a commonly used practice.

But this may be changing now with the introduction of “Virtual Actors” - a new abstraction for writing distributed applications. This abstraction was introduced with the Orleans framework by Microsoft and adopted to Java by EA with their Orbit framework.

This talk will include a short introduction to the actor model. We will then explore the Virtual Actors abstraction, how it’s different from the classic model, and why it makes distributed application programming a lot simpler.

Transcript

1. Rotem Hermon @margolis20 Actors, Evolved
2. Not THAT kind of actors.
3. Multithreading
4. The problem with multi-threaded concurrency • Shared memory and state • Race conditions • Locks and deadlocks • Blocking calls • Hard to understand and maintain • Not easily distributed
6. Threads are EVIL!
7. There has to be a better way…
8. The Actor Model • Formalized in 1973 (Carl Hewitt) • Concurrency by Message Passing • Avoids problems of threading and locking
9. An Actor, Carl Hewitt definition • The fundamental unit of computation that embodies: • Processing • Storage • Communication • An actor can: • Create new Actors • Send messages to Actors • Designate how to handle the next message
10. An Actor • Lightweight • Never shares state • Communicates through asynchronous messages • Mailbox buffers incoming messages • Processes one message at a time
11. An Actor • Lightweight • Never shares state • Communicates through asynchronous messages • Mailbox buffers incoming messages • Processes one message at a time • Single threaded
12. The Actor Model • Higher abstraction level • Simpler concurrent programming model • Write single-threaded code (easier to understand) • Concurrency and scale via actor instances • Maximizes CPU utilization • Easy to distribute
13. (Actors are actually Nanoservices)
14. Leading Classic Actor Implementations • Erlang • Developed in the late 90s by Ericsson for HA telecom exchanges • Actors are a core language feature • Akka • A JVM (Scala/Java) Actor framework library • Started by Jonas Bonér in 2009 • Became part of Typesafe (company behind Scala) • .NET port in progress since 2014 (Akka.NET)
15. Akka Fundamentals Actors Contains: • State • Behavior • An actor can “switch” its internal behavior • Mailbox • Several types of mailboxes • Children • An actor is “responsible” for other actors it creates - Supervisor
16. Akka Fundamentals • Actors form an hierarchical structure
17. Akka Fundamentals • Actor Lifecycle • Actors needs to be created and destroyed • Fault handling is done via supervision hierarchies • Several available supervision strategies
18. Akka Fundamentals • Location Transparency • Actors can be created remotely • Actors are called via an actor reference, same for local and remote • Akka Clustering for additional features
19. Akka Fundamentals • Dispatchers • Schedules the message delivery to actors (code execution) • Can be shared across actors • Several types of dispatchers and configurations
20. Akka Fundamentals • Routers • An actor that routes messages to other actors • Several routing strategies
22. There has to be a better way…
23. Virtual Actors • A simplified Actors implementation with a higher abstraction level • Introduced by Microsoft Research – Project Orleans • Goals: • Make distributed application programming easier • Prefer developer productivity and transparent scalability • “A programming model and runtime for building cloud native services”
24. Virtual Actors • A Virtual Actor: always exists and never fails
25. Virtual Actors Actor types: • Worker • An auto-scaling processing unit – multiple instances created by framework as needed
26. Virtual Actors Actor types: • Single Activation • Guaranteed to have a single active instance in the cluster
27. Virtual Actors Actor types: • Single Activation • Guaranteed to have a single active instance in the cluster • A Stateful application middle-tier!
28. A Short Example… URL Shortener Service • Shorten (URI) • Expand (ShortURI)
29. A Short Example… URL Shortener Service The Classic way shrt.uri Stateless Service DB Cache Fetch from DB Set in Cache Expand Return URL Get From Cache
30. A Short Example… URL Shortener Service The Virtual Actor way shrt.uri Expand Return URL Virtual Actors Service Worker URLActor (“shrt.uri”) “URL” DB Fetch from DB
31. A Short Example… URL Shortener Service The Virtual Actor way shrt.uri Expand Return URL Virtual Actors Service Worker URLActor (“shrt.uri”) “URL”
32. A Short Example… URL Shortener Service The Virtual Actor way shrt.uri Expand Return URL Virtual Actors Service Worker URLActor (“shrt.uri”) “URL” And logic!
33. Virtual Actor Framework • A runtime providing virtual “actor space”, analogues to virtual memory • Handles Actor placement, activation and GC when needed • Balances resources across the cluster, provides elastic scalability
34. Virtual Actor Framework Node Node Node Node Node Node
35. Virtual Actor Framework
36. Virtual Actor Framework User #21 User #73 Game #254 Game #33
37. Virtual Actor Framework Auto Scaling
38. Virtual Actor Framework Auto Scaling
39. Virtual Actor Framework Auto Scaling
40. Virtual Actor Framework Auto Scaling
41. Virtual Actor Framework Failure Recovery
42. Virtual Actor Framework Failure Recovery
43. Virtual Actor Framework Failure Recovery
44. Simplified Programming Model • An Actor is a class, implementing an interface with asynchronous methods • The caller of an Actor uses the actor interface via a proxy • Messaging is transparent and handled by the runtime. Programmers deal with interfaces and methods
45. Simplified Programming Model
46. Simplified Programming Model
47. Orleans is an important step in furthering a goal of the Actor Model that application programmers need not be so concerned with low-level system details. Carl Hewitt, Actor Model of Computation for Scalable Robust Information Systems, 2015
48. Use Cases • Stateful Services • Smart Cache • Modeling objects at scale (games, IoT) • Protecting resources / Aggregations
49. Virtual Actor Implementations • Orleans (.NET) • Started by Microsoft Research in 2011, in production since 2012 • Service high scale services on Azure (Halo 4 cloud services) • Open sourced in January 2015, active community • Orbit (Java) • Developed by BioWare (division of Electronic Arts) • Inspired by Orleans (“not a port but a re-write”) • Powering online game services • Azure Service Fabric (Reliable Actors)
51. Virtual Actors (Orleans) • Focus on simplicity and productivity • Implicit lifecycle, handled by runtime • Automatic clustering and load balancing • No hierarchy, all actors are directly accessible • Actor interfaces are regular interfaces (standard OOP) Classic Actors (Akka) • Provide full power (exposing complexity) • Explicit lifecycle, handled by programmer • Clustering and load balancing available (but more complex) • Actors are hierarchical and accessible by path • Actors communicates via explicit message classes
52. Virtual Actors (Orleans) Choose if: • Need a simple model for distributed applications • Automatic and straightforward scaling • Development team with varied levels of experience Classic Actors (Akka) Choose if: • Need full power – complex topologies, fine grain failure handling, dynamic changing of behavior, explicit message handling • Experienced development team
54. Some more about Actors and (Micro)services
55. A single Actors universe?
56. Back to microservices
57. Actor based microservices Service A Service B ServiceB Interface Actor IMyServiceB
58. Actor based microservices Service A Service B ServiceB Interface Actor IMyServiceB ServiceB HTTP Listener
59. Actor based microservices Service A Service B ServiceB Interface Actor IMyServiceB ServiceB Client ServiceB HTTP Listener JSON over HTTP
61. Thank You! Rotem Hermon @margolis20 VP Architecture @ Gigya