deploy.rb rolling restart with unicorn deploy.rb in your rails app /config/deploy.rb on your server: /etc/unicorn/site.conf /etc/init.d/unicorn /etc/nginx/sites-available/sitename.conf

deploy.rb

require "bundler/capistrano"
load 'deploy/assets'

# Pretty colors
require 'capistrano_colors'

# rbenv and ssh forwarding
set :default_environment, { 'PATH' => "$HOME/.rbenv/shims:$HOME/.rbenv/bin:$PATH" }
set :default_run_options, { :pty => true, :shell => '/bin/zsh' }
set :ssh_options, { :forward_agent => true }

set :scm_verbose, true
set :scm, :git
set :branch, 'live'

set :keep_releases, 2
set :use_sudo, false
set :deploy_via, :remote_cache

set :user, ENV['OBTVSE_USER']
set :application, ENV['OBTVSE_APP']
set :domain, ENV['OBTVSE_DOMAIN']
set :repository,  "ssh://#{user}@#{domain}/var/git/#{application}.git"
set :deploy_to, "/var/www/#{application}.com/web"
set :rails_env, 'production'

set :unicorn_config, "#{current_path}/config/unicorn/production.rb"
set :unicorn_binary, "bundle exec unicorn_rails -c #{unicorn_config} -E #{rails_env} -D"
set :unicorn_pid, "#{current_path}/tmp/pids/unicorn.pid"

role :web, domain
role :app, domain
role :db,  domain, :primary => true # This is where Rails migrations will run

after 'deploy:symlink', 'deploy:symlink_database'
after 'deploy:update', 'deploy:cleanup'

namespace :deploy do
  task :restart, :roles => :app, :except => { :no_release => true } do
    run "if [ -f #{unicorn_pid} ]; then kill -s USR2 `cat #{unicorn_pid}`; fi"
  end

  task :force_restart, :roles => :app, :except => { :no_release => true } do
    stop
    start
  end

  task :stop, :roles => :app, :except => { :no_release => true } do
    run "if [ -f #{unicorn_pid} ]; then kill -s QUIT `cat #{unicorn_pid}`; fi"
  end

  task :start, :roles => :app do
    run "cd #{current_path} && #{unicorn_binary}"
  end

  task :symlink_database, :roles => :app do
    run "cd #{current_path}/config && ln -s #{current_path}/../../shared/config/database.yml ."
  end
end

site.conf

RAILS_ENV=production
RAILS_ROOT=/var/www/site.com
APP_USER=username

sitename.conf

upstream unicorn {
  server unix:/var/www/example.com/web/current/tmp/sockets/example.sock;
}

server {
  listen 80 default;
  server_name example.com www.example.com;

  root /var/www/example.com/web/current/public;

  location ~ ^/(assets|fonts)/  {
    root /var/www/example.com/web/current/public;
    expires max;
    break;
  }

  location / {
    proxy_set_header   Host             $host;
    proxy_set_header   X-Real-IP        $remote_addr;
    proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;
    proxy_redirect off;

    proxy_pass http://unicorn;
  }

}

unicorn

#!/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: Start the unicorns at boot
# Description:       Enable Rails applications with unicorn at boot time.
### END INIT INFO

# This is /etc/init.d/unicorn (without .sh)
# init.d script for single or multiple unicorn installations. Expects at least one .conf
# file in /etc/unicorn
#
# Modified again by http://github.com/natew
# Modified by http://github.com/ganta
# based on modified version by http://github.com/zewelor
# which is based on:
#   http://gist.github.com/2623205 by http://github.com/zewelor
#   http://gist.github.com/504875  by http://github.com/jaygooby
#   http://gist.github.com/308216  by http://github.com/mguterl
#
## A sample /etc/unicorn/my_app.conf
##
## RAILS_ENV=production
## RAILS_ROOT=/var/apps/www/my_app/current
## UNICORN="/opt/rbenv/shims/unicorn_rails"
## APP_USER="www-data"
#
# This configures a unicorn master for your app at /opt/my_app/current running in
# production mode. It will read config/unicorn.rb for further set up.
#
# You should ensure different ports or sockets are set in each config/unicorn.rb if
# you are running more than one master concurrently.
#
# If you call this script without any config parameters, it will attempt to run the
# init command for all your unicorn configurations listed in /etc/unicorn/*.conf
#
# /etc/init.d/unicorn start # starts all unicorns
#
# If you specify a particular config, it will only operate on that one
#
# /etc/init.d/unicorn start my_app

RBENV_FILE_TO_SOURCE=/etc/profile.d/rbenv.sh

sig () {
    test -s "$PID" && kill -$1 `cat "$PID"`
}

oldsig () {
    test -s "$OLD_PID" && kill -$1 `cat "$OLD_PID"`
}

cmd () {
    case $1 in
        start)
            sig 0 && echo >&2 "Already running" && return 0
            su - $APP_USER -c "$CMD"
            echo "Starting"
            ;;
        stop)
            sig QUIT && echo "Stopping" && return 0
            echo >&2 "Not running"
            ;;
        force-stop)
            sig TERM && echo "Forcing a stop" && return 0
            echo >&2 "Not running"
            ;;
        restart|reload)
            sig USR2 && sleep 5 && oldsig QUIT && echo "Killing old master" `cat $OLD_PID` && return 0
            echo >&2 "Couldn't reload, starting '$CMD' instead"
            eval $CMD
            ;;
        upgrade)
            sig USR2 && echo Upgraded && return 0
            echo >&2 "Couldn't upgrade, starting '$CMD' instead"
            eval $CMD
            ;;
        rotate)
            sig USR1 && echo rotated logs OK && return 0
            echo >&2 "Couldn't rotate logs" && return 1
            ;;
        *)
            echo >&2 "Usage: $0 <start|stop|restart|upgrade|rotate|force-stop>"
            exit 1
            ;;
    esac
}

setup () {
    CONFIG=$1

    export APP_NAME=`basename $1 .conf`

    echo "Launching ${APP_NAME}"

    if [ -z $APP_USER ]; then
        if [ `getent passwd | awk -F: '{ print $1 }' | grep "^${APP_NAME}$" | wc -l` -eq 1 ]; then
            export APP_USER=$APP_NAME
        else
            echo "The is no user defined in ${CONFIG}, and the is no user in the system called ${APP_NAME}"
            return 1
        fi
    fi
    if [ -z $RAILS_ROOT ]; then
        if [ -d "/home/${APP_USER}/www/current" ]; then
            export RAILS_ROOT="/home/${APP_USER}/www/current"
        else
            echo "Rails root is not defined in ${CONFIG}"
            return 1
        fi
    fi

    if [ -z $RAILS_ENV ]; then
        export RAILS_ENV="production"
    fi

    # If unicorn binary was not defined in config
    if [ -z $UNICORN ]; then
        UNICORN="unicorn_rails"
    fi

    cd $RAILS_ROOT || return 1
    export PID=$RAILS_ROOT/tmp/pids/unicorn.pid
    export OLD_PID="$PID.oldbin"

    CMD="cd ${RAILS_ROOT} && /home/nwienert/.rbenv/shims/bundle exec unicorn_rails -E ${RAILS_ENV} c ${RAILS_ROOT}/config/unicorn.rb -D"
    return
}

# either run the start/stop/reload/etc command for every config under /etc/unicorn
# or just do it for a specific one

# $1 contains the start/stop/etc command
# $2 if it exists, should be the specific config we want to act on
source $RBENV_FILE_TO_SOURCE

if [ $2 ]; then
    . /etc/unicorn/$2.conf
    setup "/etc/unicorn/$2.conf"
    if [ $? -eq 1 ]; then
        exit 1
    fi
    cmd $1
else
    for CONFIG in /etc/unicorn/*.conf; do
        # clean variables from prev configs
        unset APP_USER
        unset RAILS_ROOT
        unset RAILS_ENV
        unset UNICORN

        # import the variables
        . $CONFIG
        setup $CONFIG
        if [ $? -eq 1 ]; then
            continue
        fi
        # run the start/stop/etc command
        cmd $1
    done
fi