Creating an Akka fat Jar

Question

I need to create a Nutch plugin that communicate with some external applications using Akka. In order to do this, I need to package the plugin as a fat Jar - I am using sbt-assembly version 0.8.3.

When I try to run the plugin, I get the exception

com.typesafe.config.ConfigException$Missing: No configuration setting found for key 'akka'

as if Akka was not able to find reference.conf. This is weird, because sbt-assembly should be able to package that file correctly, and in fact I can see its content in the created jar.

My build.sbt looks like this:

import AssemblyKeys._

name := "my-project"

version := "0.1-SNAPSHOT"

scalaVersion := "2.10.0"

resolvers ++= Seq(
  "Central Repo" at "http://repo1.maven.org/maven2",
  "Typesafe Repository" at "http://repo.typesafe.com/typesafe/releases/",
  "Akka io" at "http://akka.io/repository"
)

libraryDependencies ++= Seq(
  ...,
  "com.typesafe.akka" %% "akka-actor" % "2.1.1",
  "com.typesafe.akka" %% "akka-remote" % "2.1.1"
)

seq(assemblySettings: _*)

mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
  {
    case "plugin.xml" =>
      MergeStrategy.first
    case x if x startsWith "org/apache/jasper" =>
      MergeStrategy.last
    case x if x startsWith "javax/xml" =>
      MergeStrategy.last
    case x if x startsWith "javax/servlet" =>
      MergeStrategy.last
    case x if x startsWith "org/apache/commons" =>
      MergeStrategy.last
    case x if x startsWith "org/apache/xmlcommons" =>
      MergeStrategy.last
    case x if x startsWith "org/xml/sax" =>
      MergeStrategy.last
    case x if x startsWith "org/w3c/dom" =>
      MergeStrategy.last
    case x => old(x)
  }
}

The last lines are needed to fix some conflicts between nutch and hadoop.

What is the correct way to package an Akka application?

Kurt

The akka documentation has a warning about assembly: doc.akka.io/docs/akka/snapshot/general/configuration.html Search for When using JarJar, OneJar, Assembly or any jar-bundler. I am not sure if it helps your case – Indigo

Yes, the link I include in my question points to an entry in the Let it crash! blog where this issue is discussed. In theory, the default configuration of sbt-assembly' should merge the reference.conf` files - in fact I can see the result of a merge in the jar. But it seems that whatever merge strategy I use, the key akka is missing, that is, the file reference.conf is not read at all. – Kurt

Does it also include the contents of the reference.conf that is located in the akka-actor jar? – Indigo

Yes. It actually includes a file whose content is the concatenation of reference.conf in akka-actor and the one in akka-remote. – Kurt

it would help to show or inspect the actual stack trace, since the precise error message does not match the “usual” problem (in that akka.version is missing; in your case it is only akka) – Wooten

Answer 1

The latest version of sbt-assembly as of Nov 2013 is 0.10.1 for sbt 0.13. Using this, I was able to create a fat jar using the latest stable Akka 2.2.3 using the default merge strategy.

Files

project/build.properties:

sbt.version=0.13.0

project/assembly.sbt:

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.10.1")

assembly.sbt:

import AssemblyKeys._

assemblySettings

build.sbt:

name := "sbt-assembly-akka-sample"

version := "0.1.0-SNAPSHOT"

scalaVersion := "2.10.3"

libraryDependencies ++= Seq(
  "com.typesafe.akka" %% "akka-actor" % "2.2.3",
  "com.typesafe.akka" %% "akka-remote" % "2.2.3"
)

src/main/scala/actor.scala:

package hello

import akka.actor.{Actor, Props}
import akka.event.Logging

class MyActor extends Actor {
  val log = Logging(context.system, this)
  def receive = {
    case "test" ⇒ log.info("received test")
    case _      ⇒ log.info("received unknown message")
  }
}

src/main/scala/app.scala:

package hello

object Main extends App {
  import akka.actor.{ActorSystem, Props}
  val system = ActorSystem("mySystem")
  val myActor = system.actorOf(Props[MyActor], "myactor")
  myActor ! "test"
}

Output

Here's what I got by running assembly:

> assembly
[info] Updating {file:/xxx/sbt-assembly-01/}sbt-assembly-01...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Compiling 2 Scala sources to /xxx/sbt-assembly-01/target/scala-2.10/classes...
[info] Including: uncommons-maths-1.2.2a.jar
[info] Including: protobuf-java-2.4.1.jar
[info] Including: config-1.0.2.jar
[info] Including: netty-3.6.6.Final.jar
[info] Including: akka-remote_2.10-2.2.3.jar
[info] Including: akka-actor_2.10-2.2.3.jar
[info] Passed: Total 0, Failed 0, Errors 0, Passed 0
[info] No tests to run for test:test
[info] Including: scala-library-2.10.3.jar
[info] Checking every *.class/*.jar file's SHA-1.
[info] Merging files...
[warn] Merging 'META-INF/NOTICE.txt' with strategy 'rename'
[warn] Merging 'META-INF/license' with strategy 'rename'
[warn] Merging 'META-INF/LICENSE.txt' with strategy 'rename'
[warn] Merging 'META-INF/MANIFEST.MF' with strategy 'discard'
[warn] Merging 'reference.conf' with strategy 'concat'
[warn] Strategy 'concat' was applied to a file
[warn] Strategy 'discard' was applied to a file
[warn] Strategy 'rename' was applied to 3 files
[info] SHA-1: 1e9dcebeddc8e2a7d41a0c55a663f9ca0000000
[info] Packaging /xxx/sbt-assembly-01/target/scala-2.10/sbt-assembly-akka-sample-assembly-0.1.0-SNAPSHOT.jar ...
[info] Done packaging.
[success] Total time: 13 s, completed Nov 11, 2013 8:57:18 PM

And here's what it looks like running the jar:

$ java -jar target/scala-2.10/sbt-assembly-akka-sample-assembly-0.1.0-SNAPSHOT.jar
[INFO] [11/11/2013 20:59:48.265] [mySystem-akka.actor.default-dispatcher-2] [akka://mySystem/user/myactor] received test

Thales

That first configuration line has a typo; it should be "sbt.version". – Ignite