Unicorn Bash script for Zero DownTime Deployment. We can deploy as many as time on production environment without showing application down page. This gives us one extra hand to do continuos deployment and integration on live server. Things like this can't be achieved using the passenger.

unicorn_init.sh

#! /bin/bash

### BEGIN INIT INFO
# Provides:          unicorn
# Required-Start:    $local_fs $remote_fs $network $syslog
# Required-Stop:     $local_fs $remote_fs $network $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: starts the unicorn web server
# Description:       starts unicorn
### END INIT INFO

APP_ROOT="/var/www/www.example.com"
USER="deploy"
DAEMON=unicorn_rails
DAEMON_OPTS="-c $APP_ROOT/shared/config/unicorn.rb -E production -D"
NAME=unicorn
DESC="Unicorn app for $USER"
PID=/var/www/www.example.com/shared/pids/unicorn.pid

case "$1" in
  start)
        CD_TO_APP_DIR="cd $APP_ROOT/current"
        START_DAEMON_PROCESS="$DAEMON $DAEMON_OPTS"

        echo -n "Starting $DESC: "
        if [ `whoami` = root ]; then
          su - $USER -c "$CD_TO_APP_DIR > /dev/null 2>&1 && $START_DAEMON_PROCESS"
        else
          $CD_TO_APP_DIR && $START_DAEMON_PROCESS
        fi
        echo "$NAME."
        ;;
  stop)
        echo -n "Stopping $DESC: "
        kill -QUIT `cat $PID`
        echo "$NAME."
        ;;
  restart)
        echo -n "Restarting $DESC: "
        kill -s USR2 `cat $PID`
        echo "$NAME."
        ;;
  reload)
        echo -n "Reloading $DESC configuration: "
        kill -HUP `cat $PID`
        echo "$NAME."
        ;;
  *)
        echo "Usage: $NAME {start|stop|restart|reload}" >&2
        exit 1
        ;;
esac

exit