Орхан Гасимов: "Reactive Applications in Java with Akka"

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Reactive Applications in Java with Akka
by Orkhan Gasimov

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About author
Orkhan Gasimov
Software Developer
 Over 13 years in software development field
 Participated in full-cycle application development, leading development
groups with hands-on experience in a variety of programming languages
and technologies including solution design and architecture
 Applied practical usage of Java, C#, C/C++, Perl, PHP, JavaScript and
other programming languages. Designed desktop, mobile and web
applications from consumer products to N-tier systems

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Evolution of the Programming Model

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Scaling up Scaling out
• More price with each step
• Greater risk of hardware failure
causing bigger outages
• Limited upgradeability in the
future
• One unit for everything
• Much cheaper than scaling
vertically
• Easier to run fault-tolerance
• Easy to upgrade
• Parallel units enable parallel
execution
Scaling

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Reactive Applications in Java with Akka
 Reactive Manifesto
 Actor Model
 Load Balancing & Scaling
 Other Features & Available Modules

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Reactive Manifesto
 Application requirements have changed dramatically in recent years
 A few years ago a large application had
- tens of servers
- seconds of response time
- hours of offline maintenance
- gigabytes of data
 Today
- applications are deployed on everything from mobile devices to cloud-based clusters
- users expect millisecond response times and 100% uptime
- data is measured in Petabytes

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Reactive Manifesto
 Today's demands are simply not met by yesterday’s software architectures
 A coherent approach to systems architecture is needed
 All necessary aspects are already recognized individually
 We want systems that are
- Responsive
- Resilient
- Elastic
- Message Driven
 We call these Reactive Systems

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Reactive Manifesto
 Responsive: The system responds in a timely manner if at all possible. Responsiveness
means that problems may be detected quickly and dealt with effectively.
 Resilient: The system stays responsive in the face of failure. Any system that is not
resilient will be unresponsive after a failure.
 Elastic: The system stays responsive under varying workload. Reactive Systems can
react to changes in the input rate by increasing or decreasing the resources allocated to
service these inputs.
 Message Driven: Reactive Systems rely on asynchronous message-passing to establish a
boundary between components that ensures loose coupling, isolation and location
transparency. This boundary also provides the means to delegate failures as messages.

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Reactive Manifesto
 Large systems are composed of smaller ones and therefore depend on the Reactive
properties of their constituents. This means that Reactive Systems apply design principles
so these properties apply at all levels of scale, making them composable.

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Akka vs JavaEE
 No application server is required
 Vanilla JVM and core Java is enough
 JVMs can be stacked up to a Cluster
 Akka offers Actor Model instead of Object Oriented Model
- Actors are workers
- Objects are objects
 Actors are parallelized by default

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Concepts
 Let’s review some base concepts before the deep dive

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Concurrency vs Parallelism

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Concurrency vs Parallelism

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Asynchronous vs Synchronous

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Blocking vs Non-blocking

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Deadlock

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Starvation

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Live-lock

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Race Condition

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Progress Condition
 We want so called Progress Condition. These are actual non-
blocking guarantees.
 We want applications to behave
- Parallel
- Asynchronous
- Non-blocking
- Without deadlocks, starvation and live-locks
- Without race conditions

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Akka
 What is Akka?
 What does Akka bring?

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Actor Model
 An actor is a computational entity that, in response to a message it receives, can
concurrently:
- send a finite number of messages to other actors;
- create a finite number of new actors;
- designate the behavior to be used for the next message it receives.
 There is no assumed sequence to the above actions. They could be parallel!
 The Actor Model philosophy says ”everything is an actor”.
 This is similar to the ”everything is an object” philosophy, but object-oriented
software is typically executed sequentially, while the Actor Model is inherently
concurrent.

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Actor Model
 Actors are objects which encapsulate state and behavior
 They communicate exclusively by exchanging messages which are placed
into the recipient’s mailbox
 View them as persons
 While modeling a solution with actors
- envision a group of people and assign sub-tasks to them,
- arrange their functions into an organizational structure
- and think about how to escalate failure

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Actor System
 Actors come in systems and never alone
 Actors form hierarchies
 Actor can start child actors and supervise them
 Splitting tasks brings in smaller and more manageable tasks

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Actor Systems as a single Cluster

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Error Kernel Pattern

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Let It Crash

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API is very easy
 Create the ActorSystem
 Actor is a class extending UntypedActor and overriding onReceive
method
 Use ActorSystem::actorOf method to create actors
- Each actor can create child actor using getContext().actorOf method
 To send a message to Actor ActorRef::tell method is used
- you should have ActorRef (actor reference) which you will get on actor
creation or you can lookup/search for it by path

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Load Balancing & Scaling
 Dispatchers
 Mailboxes
 Routers

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Dispatchers

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Dispatchers

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Mailboxes
 Akka comes shipped with a number of mailbox implementations
- Unbounded (default)
- Bounded
- [U/B] Non-Blocking
- [U/B] Priority
- [U/B] Stable Priority (FIFO)
- [U/B] Control Aware
- Unbounded Single Consumer Only

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Routers

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Other Features & Available Modules
 Futures – functional promises that are used to retrieve the result of some concurrent operation
 Agents – provide asynchronous change of individual locations
 Remote – enable remote actor messaging between actor systems over the network
 Cluster – turn actor systems into a single cluster over the network
 I/O – module carries API for the implementation of network protocols and building higher
abstractions
 Camel – actors can now exchange messages with other systems over large number of protocols
& APIs such as HTTP, SOAP, TCP, FTP, SMTP or JMS, to mention a few
 Streams – stream processing API
 HTTP – a full server- and client-side HTTP stack on top of akka-actor and akka-stream. It's not a
web-framework but rather a more general toolkit for providing and consuming HTTP-based
services.

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R e a c t i v e
Thank You!