Linux service vs J2EE container

Using standard J2EE containers for application deployment is not always suitable option. Time to time you need to run an java application (jar file) as a server less, more light weight linux process. Using standard java -cp …. MainClass is feasible but sooner or latter you will reveal that there is something important missing. Especially if you are supposed to run multiple components in this way. I becomes relly messy and hard to manage pretty soon. On linux system there is a solution which is a lot better – run the component as a linux service.

Linux service controlling process

Lets make is simple and easy to understand. Linux service is essentially a “process” which is driven by init script and has defined API – set of standard commands for management of the underlying linux process. Those linux service commands looks as following(processor represents actual name as defined in init script, see latter):

service processor start
service processor status
service processor stop
service processor restart


That’s a lot simpler, easy to manage and monitor, right? You don’t need to know where particular jar file is located etc. Examples of init scripts can be usually located /etc/init.d/samples or just simply read scripts in /etc/init.d which contains various init scripts for different kinds of linux services already present on the system.
Linux Service wrappers
For java applications there is a bunch of projects which acts as a service wrappers. That enables you to quickly and easily turn jar file to regular linux service as a program daemon. There are wrappers even for windows OS. For some reasons I was directed to use just linux server standard tools so the reminder of this post will be about making the linux service program daemon in a common way via shell scripts.
Startup and shutdown scripts
First of all there is a necessity to create startup and shutdown script with a need to properly manage pid (process id) file accordingly. A good practice is to have a dedicated user to run a particular linux services and have them installed under /usr/local/xxx .

startup script follows:

#!/bin/sh
#
# Script parameters: [Instalation_Foleder]
#
# JAVA_HOME Must point at your Java Development Kit installation.
# Required to run the with the "debug" argument.
#
# JRE_HOME Must point at your Java Runtime installation.
# Defaults to JAVA_HOME if empty. If JRE_HOME and JAVA_HOME
# are both set, JRE_HOME is used.
#
# JAVA_OPTS (Optional) Java runtime options used when any command
# is executed.

# Check the way the script has been called and set current directory as PROCESSOR_HOME
if [ "X$1" = "X" ]
then
  cd .. >/dev/null
  pwd >/dev/null
  PROCESSOR_HOME=$PWD
  SERVICE_INVOKE="no"
else
  PROCESSOR_HOME=$1
  SERVICE_INVOKE="yes"
fi
echo PROCESSOR_HOME set to $PROCESSOR_HOME
# Load confing
source $PROCESSOR_HOME/bin/config.sh
# Check if the invocation is according to configuration [asService | asProcess]
if [ ! "$SERVICE_INVOKE" == "$RUN_AS_SERVICE" ]
then
  echo "ERROR - Invocation is not according to configuration - run as a Lunux Service= $RUN_AS_SERVICE"
  exit 6
fi
# check installation
if [ ! -d "$PROCESSOR_HOME/bin" \
-o ! -f "$PROCESSOR_HOME/bin/config.sh" \
-o ! -d "$PROCESSOR_HOME/conf" \
-o ! -d "$PROCESSOR_HOME/deploy" \
-o ! -d "$PROCESSOR_HOME/lib" \
-o ! -f "$PROCESSOR_HOME/conf/log4j.properties" \
-o ! -f "$PROCESSOR_HOME/deploy/test1-1.0-SNAPSHOT.jar" ];
then
echo
echo ERROR - Installation is not correct!
echo Expected installation package looks:
echo "$PROCESSOR_HOME/bin"
echo "$PROCESSOR_HOME/bin/config.sh"
echo "$PROCESSOR_HOME/conf"
echo "$PROCESSOR_HOME/conf/log4j.properties"
echo "$PROCESSOR_HOME/deploy"
echo "$PROCESSOR_HOME/deploy/test1-1.0-SNAPSHOT.jar"
echo "$PROCESSOR_HOME/lib"
exit 1
fi
# clean up
CLASSPATH=
JAVA_OPTS=
JAVA_PATH=
JAVA_EXEC=

# set JAVA
REQUIRED_JVM_VERSION=1.7
if [ -z "$JAVA_HOME" ];
then
  if [ -z "$JRE_HOME" ];
    then
      echo ERROR - either JAVA_HOME or JRE_HOME is not set!!!
      exit 1
    else
    echo Java JRE used $JRE_HOME
    JAVA_PATH=$JRE_HOME
  fi
else
  echo Java used $JAVA_HOME
  JAVA_PATH=$JAVA_HOME
fi

# set JAVA_EXEC
JAVA_EXEC=$JAVA_PATH/bin/java
#check Java bin
if [ ! -x "$JAVA_EXEC" ];
then
  echo Java binaries not found $JAVA_EXEC
  exit 1
fi
# checkJavaVersion
JVM_VERSION=$("$JAVA_EXEC" -version 2>&1 | awk -F '"' '/version/ {print $2}')
#echo version "$JVM_VERSION"
if [[ "$JVM_VERSION" < "$REQUIRED_JVM_VERSION" ]];
then
  echo ERROR - $JAVA_EXEC doesnt point to propper java version $REQUIRED_JVM_VERSION
  exit 1
fi
# setBDHISTP_MAIN
BDHISTP_MAIN=cz.jaksky.PROCESSOR.PROCESSOR
# setClasspath
CLASSPATH=$PROCESSOR_HOME/deploy/*:$PROCESSOR_HOME/lib/*
# echo Classpath set to: $CLASSPATH

# setJAVA_OPTS
JAVA_OPTS=-Dbdconf=$PROCESSOR_HOME/conf
JAVA_OPTS="$JAVA_OPTS -Dlog4j.configuration=file:$PROCESSOR_HOME/conf/log4j.properties"
#echo JAVA_OPTS set to: $JAVA_OPTS
# This is nasty as in the code there is hardcoded location to actual config file for the process
cd $PROCESSOR_HOME
runProgram() {
echo $JAVA_EXEC $JAVA_OPTS -classpath $CLASSPATH $BDHISTP_MAIN
$JAVA_EXEC $JAVA_OPTS -classpath $CLASSPATH $BDHISTP_MAIN & PROCESS_PID=$!
echo $PROCESS_PID > $PIDDIR/$PID_FILENAME
echo "new application instance started as process $PROCESS_PID"
}

if [ ! -f "$PIDDIR/$PID_FILENAME" ]
then
  echo "I will try to start new process ..."
  runProgram
else
  PID=$(cat $PIDDIR/$PID_FILENAME)
  if ps -p $PID >/dev/null
    then
      echo "WARNING $APP_NAME already running as process $PID"
    else
      echo "process $PID is not running - will try to start a new instance of the application"
      echo " "
      runProgram
  fi
fi
exit 0



shutdown script follows:

#!/bin/sh
# Script usage:
# this script can be invoked either directly in bin folder or from different location with passing information where to locate installation folder
#
# Check the way the script has been called and set current directory as PROCESSOR_HOME
if [ "X$1" = "X" ]
then
  cd .. >/dev/null
  pwd >/dev/null
  PROCESSOR_HOME=$PWD
  SERVICE_INVOKE="no"
else
  PROCESSOR_HOME=$1
  SERVICE_INVOKE="yes"
fi
echo PROCESSOR_HOME set to $PROCESSOR_HOME
# Load confing
source $PROCESSOR_HOME/bin/config.sh
if [ -z "$PIDDIR" ]
then
  echo "ERROR - Installation configuration file config.sh not found at $PROCESSOR_HOME/bin"
  exit 1
fi
# Load confing
source $PROCESSOR_HOME/bin/config.sh
# Check if the invocation is according to configuration [asService | asProcess]
if [ ! "$SERVICE_INVOKE" == "$RUN_AS_SERVICE" ]
then
  echo "ERROR - Invocation is not according to configuration - run as a Lunux Service= $RUN_AS_SERVICE"
  exit 6
fi
if [ -f "$PIDDIR/$PID_FILENAME" ]
then
  PID=$(cat $PIDDIR/$PID_FILENAME)
  kill $PID
  RC=$?
  rm $PIDDIR/$PID_FILENAME
  echo "Application $APP_NAME - process $PID shut down successfull"
  exit $RC
else
  echo "pid file not exist $PIDDIR/$PID_FILENAME, nothing to shut down"
  exit 0
fi


Config script
Those scripts relies on existence of installation configuration shell script – config.sh located in bin folder of installation as follows:

#!/bin/sh
RUN_AS_SERVICE="yes"
APP_NAME="Processor"
APP_LONG_NAME="Processor instance"
PIDDIR="/var/run/processor"
PID_FILENAME="processor.pid"


Startup script creates pid file located /var/run/processor – user under which the installation is running needs to have appropriate privileges.
Init.d script
Finally the init script which needs to be placed into /etc/init.d folder:

 ### BEGIN INIT INFO
# Provides: processor
# Required-Start:
# Required-Stop:
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: processor daemon
# Description: processor daemon
# This provides example about how to
# write a Init script.
### END INIT INFO
# Config to edit if needed
INSTALL_HOME=/usr/local/Processor
JAVA_HOME=/usr/java/default
SERVICE_USER="processor"
# No modification allowed from here
# Using the lsb functions to perform the operations.
. /lib/lsb/init-functions
#
# If the daemon is not there, then exit.
test -x $INSTALL_HOME/bin/startUp.sh || exit 5
test -x $INSTALL_HOME/bin/shutDown.sh || exit 5
test -x $INSTALL_HOME/bin/config.sh || exit 5
# Load confing
source $INSTALL_HOME/bin/config.sh
export JAVA_HOME
PIDFILE=$PIDDIR/$PID_FILENAME
# Process name ( For display )
NAME=$APP_NAME
CURRENT_USER=`id -nu`
start(){
  echo "Starting $NAME under $SERVICE_USER user..."
  if [ "$CURRENT_USER" == "$SERVICE_USER" ]
  then
    $INSTALL_HOME/bin/startUp.sh $INSTALL_HOME >/dev/null
    RC=$?
  else
    su --preserve-environment --command="$INSTALL_HOME/bin/startUp.sh $INSTALL_HOME >/dev/null" $SERVICE_USER
    RC=$?
  fi
}
stop(){
  echo "Stoping $NAME running under $SERVICE_USER user ..."
  if [ "$CURRENT_USER" == "$SERVICE_USER" ]
  then
    $INSTALL_HOME/bin/shutDown.sh $INSTALL_HOME >/dev/null
    RC=$?
  else
    su --preserve-environment --command="$INSTALL_HOME/bin/shutDown.sh $INSTALL_HOME >/dev/null" $SERVICE_USER
    RC=$?
  fi
}
case $1 in
start)
  start
  exit $RC
;;
stop)
  stop
  exit $RC
;;
restart)
  stop
  start
  exit $RC
;;
status)
  if [ ! -f "$PIDDIR/$PID_FILENAME" ]
  then
    echo "$NAME is NOT RUNNING"
    exit 1
  else
    PID=$(cat $PIDDIR/$PID_FILENAME)
    if ps -p $PID >/dev/null
    then
      echo "$NAME is RUNNING $PID"
      exit 0
    else
      echo "$NAME is NOT RUNNING"
      exit 1
    fi
  fi
;;
*)
# For invalid arguments, print the usage message.
echo "Usage: $0 {start|stop|restart|status}"
exit 2
;;
esac


In the init script there is a need to change to appropriate java apps installation folder JAVA_HOME if not default and SERVICE_USER to user which is supposed to run this service. Service can be started under root account or SERVICE_USER without password specification or any other user with knowledge of credentials.
Conclusion
If you have a production like experience with java service wrappers mentioned at the beginning of the article don’t hesitate and share it! This way it serves the purpose at given situation.
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