This repository contains an Akka kata to be used during the Stockholm Scala Meetup group (or whenever you feel like doing some Akka Karate related training).
- A computer
- An installed OS
- Java
- SBT 0.12.0
- Git (not mandatory)
So you decided to install Git (or already had it installed). Smart move! Open a terminal and type:
> git clone git://github.com/henrikengstrom/akka-meetup-sthlm.git
Open a browser and point it to:
https://github.com/henrikengstrom/akka-meetup-sthlm/downloads
Select your preferred flavor of compression (zip or tar.gz), download and extract onto your machine.
To compile your project code with SBT:
> sbt compile
Open a terminal and type:
> sbt eclipse
Open Eclipse and point it to the project catalogue.
Open a terminal window and type:
> sbt gen-idea
Open IntelliJ and point it to the project catalogue.
The aim with this kata is to show some core elements of Akka:
- Remoting
- Supervision
- Some Akka patterns
To showcase the elements above we have selected to implement a simple betting application - or at least provide a skeleton of such an application. The implemented application should simulate a transacted system, i.e. it should handle a crash of a JVM. We will discuss pros and cons of alternative implementations during the meetup.
The application you create will run in two different JVMs (and actor systems). One "node", called betting service, receives bet messages from a client, creates a transaction number and sends this message to the other "node" betting processor. The betting service keeps track of messages sent and should also handle confirmation messages from the betting processor. It also handles re-sending of messages that have not been confirmed.
The task of the betting processor is to spawn workers that do the dangerous job (in this case interacting with an unstable service), supervise these workers and send back confirmation that a task has been performed.
The betting service should be able to function without any available betting processor, i.e. should it receive bet(s) before the betting processor has registered it should keep these bets locally and send them as soon as a betting processor becomes available.
Sometimes your servers crash(!) and therefore you should design with this in mind. Sending too many bets to the betting processor will cause it (the JVM) to crash. It is an essential part of this kata to make sure that the betting service can handle such a crash.
We will provide some alternative implementations to show how to solve the different tasks/assignments raised in the code (see comments in provided code).
To start the betting service and the betting processor you should create some start scripts. This is easily done by using with the command:
> sbt start-script
This will create bash scripts in service/target/start, processor/target/start and client/target/start. To start things you just have to run the scripts from different command prompts in the top level project directory starting with service followed by processor.
If you're on Windows without access to a bash shell then you will have to copy the command line and arguments into a script of your own, and rewrite the paths to windows style paths.
Do not place the scripts in a target directory since they will be deleted if you do:
> sbt clean
To start testing your application you can issue the command:
> client/target/start send
And to check the results you issue the command:
> client/target/start
Remember to clean out the persistent store of bets in between runs of your system. It is stored in the file persistent_store in the top level project directory.
For a small collection of akka information useful for this kata see Green Belt Akka
- Henrik Engström : @h3nk3
- Björn Antonsson : @bantonsson
Props to Typesafe for paying for the time taken to implement this kata example.