Microkernel
The purpose of the Akka Microkernel is to offer a bundling mechanism so that you can distribute an Akka application as a single payload, without the need to run in a Java Application Server or manually having to create a launcher script.
Warning
Akka Microkernel will be deprecated and removed. It will be replaced by using an ordinary user defined main class and packaging with sbt-native-packager or Typesafe ConductR.
To run an application with the microkernel you need to create a Bootable class that handles the startup and shutdown the application.
The code for the Hello Kernel example (see the HelloKernel class for an example
of creating a Bootable):
package sample.kernel.hello
import akka.actor.{ Actor, ActorSystem, Props }
import akka.kernel.Bootable
case object Start
class HelloActor extends Actor {
val worldActor = context.actorOf(Props[WorldActor])
def receive = {
case Start => worldActor ! "Hello"
case message: String =>
println("Received message '%s'" format message)
}
}
class WorldActor extends Actor {
def receive = {
case message: String => sender() ! (message.toUpperCase + " world!")
}
}
class HelloKernel extends Bootable {
val system = ActorSystem("hellokernel")
def startup = {
system.actorOf(Props[HelloActor]) ! Start
}
def shutdown = {
system.shutdown()
}
}
sbt-native-packager is the recommended tool for creating distributions of Akka applications when using sbt.
Define sbt version in project/build.properties file:
sbt.version=0.13.7
Add sbt-native-packager in project/plugins.sbt file:
addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "1.0.0-RC1")
Use the package settings and specify the mainClass in build.sbt file:
import NativePackagerHelper._
name := "hello-kernel"
version := "0.1"
val akkaVersion = "2.3.16"
libraryDependencies ++= Seq(
"com.typesafe.akka" %% "akka-kernel" % akkaVersion,
"com.typesafe.akka" %% "akka-actor" % akkaVersion,
"com.typesafe.akka" %% "akka-slf4j" % akkaVersion,
"ch.qos.logback" % "logback-classic" % "1.0.7"
)
mainClass in Compile := Some("akka.kernel.Main")
enablePlugins(JavaServerAppPackaging)
mappings in Universal ++= {
// optional example illustrating how to copy additional directory
directory("scripts") ++
// copy configuration files to config directory
contentOf("src/main/resources").toMap.mapValues("config/" + _)
}
// add 'config' directory first in the classpath of the start script,
// an alternative is to set the config file locations via CLI parameters
// when starting the application
scriptClasspath := Seq("../config/") ++ scriptClasspath.value
Note
Use the JavaServerAppPackaging. Don't use AkkaAppPackaging (previously named
packageArchetype.akka_application, since it doesn't have the same flexibility and quality
as the JavaServerAppPackaging.
Use sbt task dist package the application.
To start the application (on a unix-based system):
cd target/universal/
unzip hello-kernel-0.1.zip
chmod u+x hello-kernel-0.1/bin/hello-kernel
hello-kernel-0.1/bin/hello-kernel sample.kernel.hello.HelloKernel
Use Ctrl-C to interrupt and exit the microkernel.
On a Windows machine you can also use the bin\hello-kernel.bat script.
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