SSH into Root
$ ssh [email protected]
Change Root Password
$ passwd
Add Deploy User
$ adduser apps
Update Sudo Privileges
$ visudo
apps ALL=(ALL:ALL) ALL
Configure SSH
$ vi /etc/ssh/sshd_config
Port 22 # Change (1025..65536)
Protocol 2 # Change
PermitRootLogin no  # Change
UseDNS no # Add
AllowUsers deployer # Add
Reload SSH
$ reload ssh
SSH with Deploy User (Don't close root)
$ ssh -p {port_number} [email protected]
Install Curl
$ sudo apt-get update
$ sudo apt-get install curl
Install RVM
$ curl -L get.rvm.io | bash -s stable
$ source ~/.rvm/scripts/rvm
$ rvm requirements
$ rvm install 2.3.0
$ rvm use 2.3.0 --default
$ rvm rubygems current
Install PostgreSQL
$ sudo apt-get install postgresql $ sudo apt-get install ruby-dev build-essential $ sudo apt-get install postgresql-client libpq5 libpq-dev
Create Postgres User
$ sudo -u postgres psql
create user apps with password '{password}';
alter role apps superuser createrole createdb replication;
create database {db_name} owner apps;
Install GIT
$ sudo apt-get install git-core
Install Bundler
$ gem install bundler
Intsall Javasript Runtime
$ sudo apt-get install nodejs
Install ImageMagick/GraphicsMagick
$ sudo apt-get install imagemagick libmagickwand-dev
Setup Nginx
$ sudo apt-get install nginx
$ nginx -h
$ cat /etc/init.d/nginx
$ /etc/init.d/nginx -h
$ sudo service nginx start
$ sudo vim /etc/nginx/sites-enabled/default
upstream unicorn {
  server unix:/tmp/unicorn.MYAPP.sock fail_timeout=0;
}
server {
  listen 80 default deferred;
  # server_name example.com;
  root /home/deployer/apps/MYAPP/current/public;
  location ^~ /assets/ {
    gzip_static on;
    expires max;
    add_header Cache-Control public;
  }
  location ~ ^/(robots.txt|sitemap.xml.gz)/ {
    root /home/deployer/apps/MYAPP/current/public;
  }
  try_files $uri/index.html $uri @unicorn;
  location @unicorn {
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_redirect off;
    proxy_pass http://unicorn;
  }
  error_page 500 502 503 504 /500.html;
  client_max_body_size 4G;
  keepalive_timeout 10;
}
Add Unicorn
$ vim Gemfile
gem 'unicorn'    
Update Unicorn Config
$ vim config/unicorn/production.rb
root = "/home/deployer/apps/MYAPP/current"
working_directory root
pid "#{root}/tmp/pids/unicorn.pid"
stderr_path "#{root}/log/unicorn.log"
stdout_path "#{root}/log/unicorn.log"
worker_processes Integer(ENV['WEB_CONCURRENCY'])
timeout 30
preload_app true
listen '/tmp/unicorn.spui.sock', backlog: 64
before_fork do |server, worker|
  Signal.trap 'TERM' do
    puts 'Unicorn master intercepting TERM and sending myself QUIT instead'
    Process.kill 'QUIT', Process.pid
  end
  defined?(ActiveRecord::Base) and
    ActiveRecord::Base.connection.disconnect!
end
after_fork do |server, worker|
  Signal.trap 'TERM' do
    puts 'Unicorn worker intercepting TERM and doing nothing. Wait for master to send QUIT'
  end
  defined?(ActiveRecord::Base) and
    ActiveRecord::Base.establish_connection
end
# Force the bundler gemfile environment variable to
# reference the capistrano "current" symlink
before_exec do |_|
  ENV['BUNDLE_GEMFILE'] = File.join(root, 'Gemfile')
end
Add Capistrano
$ vim Gemfile
group :development do
  gem 'capistrano-rails'
  gem 'capistrano-rvm'
  gem 'capistrano3-unicorn'
end
Install Capistrano
$ bundle exec cap install
Update Capistrano Capfile
$ vim Capfile
require 'capistrano/setup'
require 'capistrano/deploy'
require 'capistrano/rvm'
require 'capistrano/bundler'
require 'capistrano/rails/assets'
require 'capistrano/rails/migrations'
require 'capistrano3/unicorn'
# Load custom tasks from `lib/capistrano/tasks' if you have any defined
Dir.glob('lib/capistrano/tasks/*.rake').each { |r| import r }
Update Capistrano Deploy Config
$ vim config/deploy.rb
lock '3.3.5'
set :application, 'spui'
set :repo_url, '[email protected]:MYGITHUB/MYAPP.git'
ask :branch, proc { `git rev-parse --abbrev-ref HEAD`.chomp }.call
set :use_sudo, false
set :bundle_binstubs, nil
set :linked_files, fetch(:linked_files, []).push('config/database.yml')
set :linked_dirs, fetch(:linked_dirs, []).push('log', 'tmp/pids', 'tmp/cache', 'tmp/sockets', 'vendor/bundle', 'public/system')
after 'deploy:publishing', 'deploy:restart'
namespace :deploy do
  task :restart do
    invoke 'unicorn:reload'
  end
end
Update Production Deploy Config
$ vim config/deploy/production.rb
set :port, 22
set :user, 'deployer'
set :deploy_via, :remote_cache
set :use_sudo, false
server '123.333.333.333',
  roles: [:web, :app, :db],
  port: fetch(:port),
  user: fetch(:user),
  primary: true
set :deploy_to, "/home/#{fetch(:user)}/apps/#{fetch(:application)}"
set :ssh_options, {
  forward_agent: true,
  auth_methods: %w(publickey),
  user: 'deployer',
}
set :rails_env, :production
set :conditionally_migrate, true    
Add SSH Key to DigitalOcean
$ cat ~/.ssh/id_rsa.pub | ssh -p 22 [email protected] 'cat >> ~/.ssh/authorized_keys'
Say Hi to Github
# follow the steps in this guide if receive permission denied(public key)
# https://help.github.com/articles/error-permission-denied-publickey
$ ssh [email protected]    
Check Deployment (Commit and Push)
$ cap production deploy:check
Deploy
$ cap production deploy
Thanks to James Dullaghan for his help.