Deploying, starting and stopping Scala applications on a remote server

Question

What the preferred way is to deploy Scala applications on a remote Linux server.

This is a fairly simple, but limited, way of deploying a Scala app on a remote server (nice for quick testing of not-so-sensitive projects):

1. From the remote server I pull my source from git
2. Using the sbt-assembly plug-in I build a jar on the server

3. I then run the Scala application using nohup, which allows you to exit the remote session without terminating the process:

   nohup java -jar myapp.jar > myapp.log 2> myapp.err < /dev/null &

Firstly, what is the best way to stop the process once it is running, considering it's using resources such as databases etc. Do I just lookup the java process id and nuke it?

Secondly, what is the best way to start a java application automatically on restart. I recall using init.d in the past, but remember getting some uphill since it was a java application.

Update:

I missed the elephant in the room here. I'm using the Spray library, which in turns uses Akka, so that provides a number of interesting options.

Answer 1

There is a number of ways to skin a cat...

You could use the sbt-start-script https://github.com/sbt/sbt-start-script or even sbt-native-packager https://github.com/sbt/sbt-native-packager

You could wrap Spray's Boot example script in a simple init.d script that calls sbt as detailed in this answer https://stackoverflow.com/a/17399574/155689, or just use the plain nohup java command.

You could create larger daemon aware classes and scripts, or extend those with init.d scripts that use Jsvc http://commons.apache.org/proper/commons-daemon/jsvc.html or Java Service Wrapper. http://wrapper.tanukisoftware.com/

An example of a daemon and application class:

package com.example.myapplication.server

import akka.actor.{Props, ActorSystem}
import spray.can.Http
import akka.io.IO
import com.example.myapplication.api.MyServiceActor
import org.apache.commons.daemon._

trait ApplicationLifecycle {
  def start(): Unit
  def stop(): Unit
}

abstract class AbstractApplicationDaemon extends Daemon {
  def application: ApplicationLifecycle

  def init(daemonContext: DaemonContext) {}

  def start() = application.start()

  def stop() = application.stop()

  def destroy() = application.stop()
}

class ApplicationDaemon() extends AbstractApplicationDaemon {
  def application = new Application
}

object ServiceApplication extends App {

  val application = createApplication()

  def createApplication() = new ApplicationDaemon

  private[this] var cleanupAlreadyRun: Boolean = false

  def cleanup(){
    val previouslyRun = cleanupAlreadyRun
    cleanupAlreadyRun = true
    if (!previouslyRun) application.stop()
  }

  Runtime.getRuntime.addShutdownHook(new Thread(new Runnable {
    def run() {
      cleanup()
    }
  }))

  application.start()
}


class Application() extends ApplicationLifecycle with Logging {

  private[this] var started: Boolean = false

  private val applicationName = "MyApplication"

  implicit val actorSystem = ActorSystem(s"$applicationName-system")

  def start() {
    logger.info(s"Starting $applicationName Service")

    if (!started) {
      started = true

      val myService = actorSystem.actorOf(Props[MyServiceActor], "my-service")

      IO(Http) ! Http.Bind(myService, interface = "0.0.0.0", port = 8280)
    }
  }

  def stop() {
    logger.info(s"Stopping $applicationName Service")

    if (started) {
      started = false
      actorSystem.shutdown()
    }
  }

}

If you deploy the jar (use sbt-assembly for a fat jar) in /opt/myapplication/myapplication.jar, add some external configurations in the /etc/mycompany folder, then you can wrap that in an /etc/init.d/myapplication script, for example using Jsvc:

#!/bin/sh
### BEGIN INIT INFO
# Provides:          myapplication
# Required-Start:    $local_fs $remote_fs $network
# Required-Stop:     $local_fs $remote_fs $network
# Should-Start:      $named
# Should-Stop:       $named
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Control myapplication
# Description:       Control the myapplication daemon.
### END INIT INFO

set -e

if [ -z "${JAVA_HOME}" ]; then
        JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:/bin/java::")
fi
JAVA_OPTS="-Xms512m -Xmx1024m"

APP=myapplication

PID=/var/run/${APP}.pid
OUT_LOG=/var/log/myapplication/${APP}_out.log
ERR_LOG=/var/log/myapplication/${APP}_err.log

DAEMON_USER=yourserviceuser

APP_LOG_CONFIG=/etc/mycompany/${APP}_logback.xml
APP_CONFIG=/etc/mycompany/${APP}.conf
APP_HOME=/opt/${APP}
APP_CLASSPATH=$APP_HOME/${APP}.jar
APP_CLASS=com.example.myapplication.server.ApplicationDaemon

if [ -n "$APP_LOG_CONFIG}" ]; then
        JAVA_OPTS="-Dlogback.configurationFile=${APP_LOG_CONFIG} ${JAVA_OPTS}"
fi

DAEMON_ARGS="-home ${JAVA_HOME} -Dconfig.file=${APP_CONFIG} ${JAVA_OPTS} -pidfile ${PID} -user ${DAEMON_USER} -outfile ${OUT_LOG} -errfile ${ERR_LOG} -cp ${APP_CLASSPATH} ${APP_CLASS}"

. /lib/lsb/init-functions

case "$1" in
        start)
                log_daemon_msg "Starting ${APP}"
                cd ${APP_HOME} && jsvc ${DAEMON_ARGS}
                log_end_msg 0
                ;;
        stop)
                log_daemon_msg "Stopping ${APP}"
                cd ${APP_HOME} && jsvc -stop ${DAEMON_ARGS}
                log_end_msg 0
                ;;
        *)
                log_success_msg "Usage:  {start|stop}"
                echo "Usage:  {start|stop}"
                exit 1
                ;;
esac

exit 0

With this you can now sudo service myapplication start|stop

And if as mentioned that you want it to automatically start on boot then run this command

sudo update-rc.d myapplication defaults

This daemon approach works with the Spray apps I have.