1. Virtual Actors with Microsoft Orleans
By Daniel D’Agostino
1st August 2017

2. Introducing: Actors
Actor models

3. Multithreading
Shared
Resource
Objects
Objects
Thread 1
Thread 2

4. Actor Model
Actor
Single
Thread
Internal
State

5. Actor Model
Message Passing

6. Actor Properties Single threaded No data sharing Message passing
Not per actor, but thread pool
One message at a time (internal message queue)
No data sharing
Message passing

7. Actor Models Examples Erlang Akka Akka .NET Orleans
Azure ServiceFabric
ProtoActor

8. Introducing: Concepts Behind Microsoft Orleans
Virtual Actors

9. Grains and Silos

10. Terminology Grain: a virtual actor
Silo: a server instance, holding many grains
Turn: processing a message
Activation: single living instance of a grain

11. Activation and Life Cycle
Grains always “exist”
The runtime activates them as needed
They are deactivated automatically after an idle period or when requested
Can control what happens on activation/deactivation
Comparison with normal actors:
Control creation, full life cycle, hierarchy

12. Handling Failure No supervision hierarchies
Exceptions are thrown back to the caller
Grains on dead nodes are automatically reactivated elsewhere by the runtime

13. Location Transparency
No actor path
Just a grain ID
Actors are allocated automatically to different nodes
Typically you would not know where an actor lives
Forces you to think distributed first

14. Asynchrous Messaging No need to declare a message class
Methods provide an abstraction
Grain methods must be asynchronous
Must return Task or Task<T>
Enforced by the runtime
Invocation patterns
Await: preserves order, affects throughput
Fire and forget: parallel (faster, no ordering)

15. Finite State Machines
Not provided out of the box
Trivial to implement

16. Introducing: Orleans itself
Microsoft Orleans

17. What is Orleans? Created by Microsoft Research
Open sourced in January 2015
Virtual Actors implementation
Abstraction of actor model
Less control but much easier to work with
Used in Halo 4 and 5 among others

18. Community and Support Under active development by Microsoft
No commercial support
Active support on Gitter chat
Very good documentation
Various community-contributed plugins
OrleansContrib

19. Roadmap
Mainly working towards Orleans 2.0 with .NET Core / Standard support
Technical Preview already available

20. Deployment Built with Azure in mind Supports on-premises deployment
Pluggable components and third party integrations
Cluster membership
Storage
etc.

21. How To: Create Simple Orleans projects
Getting Started

22. Simple Orleans Projects
Get the Orleans VS Extension
Dev/Test Host

23. Full Project Structure
Purpose
Type
NuGet Package
References
Client
Console Application
Microsoft.Orleans.Client
Interfaces
Silo
Microsoft.Orleans.Server
Interfaces, Grains
Grains
Class Library
Microsoft.Orleans.Core Microsoft.Orleans.OrleansCodeGenerator.Build

24. Full Project Structure (2)
Configure garbage collection
Configure silo (endpoints)
Configure client (gateway)
Write Silo code
Write Client code
Optional: add Dashboard

25. Dashboard (Peek)

26. Intermediate concepts
How To: Do Various Cool Stuff
Intermediate concepts

27. Stateless Workers By default, grains are singletons
If marked with [StatelessWorker] attribute, multiple activations of a grain are allowed
Always local, never remote
Automatic scaling
Similar in concept to Akka routers
Activations are not individually addressable

28. Messaging Optimisations
Serialization
Default: deep copy
Immutable: pass by reference
Stateless Worker: saves remote call
Re-entrant grains
Possibility of interleaving
Not recommended
Code generation (runtime vs build-time)

29. Dependency Injection Simple built-in dependency injection
Based on ASP .NET Core model
How to:
Add startup class
Configure dependencies
Call UseStartupType<T>()
Add constructor dependencies

30. How To: Save Grain State
Grain Persistence

31. Grain Persistence Overview
Saves current state only
Event sourcing introduced very recently
State is automatically loaded on grain activation
Storage provider name specified in an attribute
Or defaults to “Default”
Configure using code or XML config

32. Grain Persistence How-To
Create class holding grain’s state
Inherit from Grain<T>
T is the grain state class
API
State property
WriteStateAsync()
ReadStateAsync()
ClearStateAsync()
StorageProvider attribute
Configure storage provider

33. Official Storage Providers
AzureTableStorage
AzureBlobStorage
DynamoDBStorageProvider
ADO .NET Storage Provider
SQL Server
MySQL / MariaDB
MemoryStorage
Volatile, for testing only
ShardedStorageProvider

34. Contributed Storage Providers
MongoDB
DocumentDB
Redis
Simple SQL Server
RavenDB
CouchBase
Firebase
Arango

35. Custom Storage Providers
Taken from:
Simple API
Optimistic Concurrency Control / Etag

36. How To: Run Tasks Periodically
Timers and reminders

37. Timers Bound to grain activation Same as System.Threading.Timer
Will not run if grain not active
Does not count towards keeping grain active
Does not span across multiple activations
Same as System.Threading.Timer
Behaves like reentrant grain
Good for low-res (e.g. seconds/minutes)

38. Reminders
Persistent
Stored in database
Runs even if grain not active
Must be explicitly cancelled
Good for higher resolution (minutes, hours, or days)

39. How To: Run Unit and Integration Tests Against Grains
Testing grains

40. Testing Approaches
Unit Testing
TestCluster

41. Unit Testing Grains
Grains are simple classes and can be unit tested as is
No need for TestProbes or AutoPilots!
Exceptions:
GrainFactory: use DI with IGrainFactory
Persistence: use DI with IStorage
GetPrimaryKey*(): use DI with workaround
Extension methods, cannot be mocked

42. TestCluster In-Memory Cluster Can test all grain interactions
Package: Microsoft.Orleans.TestingHost
Can test all grain interactions

43. On: PubSub, Distributed Systems, and More
Advanced concepts

44. Publish/Subscribe Virtual Streams Abstraction Official OrleansContrib
Observers and Observables
Explicit and Implicit Subscriptions
Official
Simple Message Stream Provider
Azure Queue Stream Provider
OrleansContrib
RabbitMQ Stream Provider

45. Cluster Membership MembershipTableGrain (testing only)
Databases via ADO .NET
Azure Table Storage
Apache ZooKeeper
Consul
DynamoDB

46. Design Patterns From OrleansContrib: Observer Cadence Reduce
Smart Cache
Dispatcher
Hub

47. Delivery and Ordering Tradeoff Delivery Guarantees Message Loss
Duplicates
Ordering (Orleans: await)
Delivery Guarantees
At Least Once (Orleans: by configuration)
At Most Once (Orleans: by default)
Exactly Once

48. How to: find more information
Wrapping up

49. Resources Orleans Homepage Halo Cloud Services presentation
Documentation & Tutorials
Halo Cloud Services presentation
Technical Report 2014
Gitter chat
Source code on GitHub
OrleansContrib

50. Question Time
Q&A