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Reactive programming with scala and akka
The document discusses reactive programming using Scala and Akka. It introduces reactive programming and why it is needed, provides a brief introduction to Scala and Akka, and discusses the four principles of reactive applications: being event-driven, resilient, scalable, and responsive. It describes how the actor model in Akka helps enable reactive applications by allowing for message-driven concurrency and fault tolerance through isolation of failures.
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Reactive programming with scala and akka
- 1. Reactive programming wwiitthhSSccaallaa aanndd AAkkkkaa Piyush Mishra Software Consultant Knoldus Software LLP
- 2. AAggeennddaa ● Reactiveprogramming and why we need it. ● Brief introduction to Scala ● Brief introduction to Akka ● Reactive applications. ● Four principles of reactive applications.
- 3. PPrreesseenntt DDaayy HHoowwddoo wwee wwrriittee aapppplliiccaattiioonnss ttooddaayy?? A Foo
- 4. PPrreesseenntt DDaayy Tillnow we program like this (new Foo).doSomething1(); (new Foo).doSomething2(); (new Foo).doSomething3(); (new Foo).printOutput Synchronous ? Blocking ? Sequential ?
- 5. Reactive programming iscompletely different from the sequential work flow. They react when something is done Worker A Done and react Worker B Done and react Worker C Done and react Output Reactive programming
- 6. Reactive pprrooggrraammmmiinngg ––WWhhyy?? Fast, faster, fastest ….. fastetstestestest ...
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- 9. What iiss rreeaaccttiivvee-- DDiisssseeccttiioonn
- 10. What iiss rreeaaccttiivvee-- DDiisssseeccttiioonn
- 11. What iiss rreeaaccttiivvee-- DDiisssseeccttiioonn
- 12. What iiss rreeaaccttiivvee-- DDiisssseeccttiioonn
- 13. What iiss rreeaaccttiivvee-- TTooggeetthheerr
- 14. Reactive – Parts– Event Driven Concurrent application uses shared memory to communicate. Thread A Thread B R/W R/W Shared memory Synchronization Non-determinism Hard to understand code
- 15. Reactive – Parts– Event Driven Event driven system avoid shared memory communication And uses message passing model throughout the Application Actor A Message Actor B Continued..
- 16. Reactive –– PPaarrttss–– EEvveenntt DDrriivveenn Sender Message Receiver Loosely coupled Easier to extend Evolve Receiver dormant till it receives message Large number of receivers share same hardware thread Low latency High throughput Lower operational costs
- 17. Reactive –– PPaarrttss–– EEvveenntt DDrriivveenn UI Web Layer Services Database Application must be reactive from top to bottom. None of the layers should stall.
- 18. Reactive –– PPaarrttss–– EEvveenntt DDrriivveenn We need to go in parallel. PERIOD!
- 19. Reactive –– PPaarrttss–– SSccaallaabbllee The word scalable is defined by Merriam- Webster as “capable of being easily expanded or upgraded on demand”
- 20. Reactive –– PPaarrttss–– SSccaallaabbllee Node 1 Actor A Node 2 Message Actor B Asynchronous message passing Location transparency The network is inherently unreliable
- 21. RReeaaccttiivvee –– PPaarrttss–– RReessiilliieenntt Isolate failures Prevent cascading failures
- 22. RReeaaccttiivvee –– PPaarrttss–– RReessiilliieenntt Node 1 Actor A Node 2 Message Actor B Loose coupling Isolated components Hierarchy of failure management
- 23. Reactive –– PPaarrttss–– RReessppoonnssiivvee Responsive is defined by Merriam- Webster as "quick to respond or react appropriately". Respond immediately Even in event of failure
- 24. Reactive –– PPaarrttss–– RReessppoonnssiivvee Response event is returned in O(1) or at least O(log n) time regardless of load How ? Batching when there is high traffic Queues bound with back pressure Failures handled with recovery and circuit breakers
- 25. RReeaaccttiivvee –– tthheewwhhoollee
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- 31. SSccaallaa BBaassiiccss 1.Scala method definitions def fun(x: Int) = { result } 2 . def fun = result 3 .Scala variable definitions var x: Int = expression val x: String = expression 1. Java method definitions Int fun(int x) { return result } 2. (no parameterless methods) 3. java variable definitions Int x = expression final String x = expression
- 32. Scala BBaassiiccss ––CCoonncciissee ccooddee
- 33. SSccaallaa BBaassiiccss pureobject system operator overloading closures mixin composition with traits special treatment of interfaces existential types abstract pattern matching static members primitive types break and continue Interfaces Wildcards raw types enums
- 34. What is Akka Akka is the framework developed by Typesafe Right abstraction with actors for concurrent, fault-tolerant and scalable applications For Fault-Tolerance uses “Let It Crash” model Abstraction for transparent distribution of load We can Scale In and Scale Out
- 35. Problem Which AkkaSolve Truly highly concurrent systems Truly scalable systems Self-healing, fault-tolerant systems
- 36. Akka Never thinkin terms of shared state, state visibility, threads, locks, concurrent collections, thread notification etc Low level concurrency becomes Simple Workflow - we only think in terms of message flows in system We get high CPU utilization, low latency, high throughput and scalability - for free as part of this model Proven and superior model for detecting and recovering from errors
- 37. Akka Main partof Akka Understanding the ACTOR model
- 38. Actor Model Messagesare in mailbox but no thread is allocated
- 39. Actor Model Actorread the message , a thread is allocated to it And it apply behavior on it and state change
- 40. Actor Model Afterprocessing thread is deallocated
- 41. DDeeffiinnee aaccttoorr Definemessage on which actor will react. case object Hello Define actor Class HelloActor extends Actor { def receive = { case Hello => println(“Hello”) case _=> println(“I did not understand”) } }
- 42. Tying it back– Event Driven Message Passing ! ?
- 43. Tying it back– Event Driven Code
- 44. Tying it back– Resilience
- 45. RReessiilliieenntt Applications whichare fault tolerant, detect failure and recover from failure are resilient. Such system are self healed and unstoppable
- 46. Actor System Guardianactor Actor A Actor B Actor C Actor D Actor System can be think of as home for actors
- 47. Actors form parentchild relationship Guardian actor Actor A Actor B /A Actor C Actor D /A/C /B /B/D
- 48. OOnnee ffoorr oonneeSSttrraatteeggyy Guardian System actor X Y z
- 49. OOnnee ffoorr oonneeSSttrraatteeggyy Guardian System actor X Y z Only x will be restated
- 50. OOnnee ffoorr aallllSSttrraatteeggyy Guardian System actor X Y z
- 51. OOnnee ffoorr aallllSSttrraatteeggyy Guardian System actor X Y z All children will be restated
- 52. Tying it back– Resilience Code
- 53. Tying it back– Scalability
- 54. SSccaallaabbllee Applications whichare able to scale up/down as the load Increases or decreases are scalable. Scaling is of two types. 1. Scaling the application on all cpu's core is called scale up. 2. Scaling the application to multiple machine is called scale out
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- 56. RReessppoonnssiivvee Application whichare able to respond even if failure occurs or load increases are responsive.
- 57. RReessppoonnssiivvee Bringing thesethree traits (event driven, resilient, and Scalable) together make to the applications responsive and all these four qualities together make the application reactive.
- 58. Reactive ppllaattffoorrmm ––ccoommppoonneennttss Play (Reactive we application framework built on top of akka) Akka Clustering Akka persistence Adaptive load balancing Software Transnational memory
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Editor's Notes
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