Ruby & PostgreSQL Vagrantfile. Constants at the top are meant to be configured on a per-project basis, with defaults that are explained in comments above each of them.

Vagrantfile

# Ruby + PostgreSQL Vagrantfile
# Written by Colby Ludwig, @cdl

# Vagrantfile for setting up a base Ruby + PostgreSQL environment on
# Ubuntu 14.04 with the latest deps. Sets up the following:
#   - rbenv for installing Ruby with the default `vagrant` user
#   - shares the current directory for the project to ~/{dir-name}
#   - sets up Postgres with a given database name and password (user is `postgres`)
#   - forwards given ports
#
# Thanks to http://stackoverflow.com/a/30106828 for helping me get the
# base of the file going.

# The Ruby version to install with rbenv. Use `rbenv install -l` to list
# all versions available to rbenv.
$ruby_version = "2.3.1"

# Project name - infers it's name from the current directory (that this Vagrantfile
# is in), but you can change the below to just a raw string if you'd like.
$project_name = File.basename(Dir.getwd)

# Locale environment to use. Change the below to match the locale used on your
# host machine. (When in doubt, stick with the default.)
$locale = "en_US.UTF-8"

# The ports to open. Points each port from the guest to the same port on the server.
# So, setting $ports to [ 8080 ] will point the VM :8080 -> host :8080.
$ports = [ 8080 ]

# The database name and password to use for Postgres. User is `postgres`.
$db_name = "db_name"
$db_password = "db_password"

# The provisioning script. Uses the variables above to properly set things up
# for a Ruby environment.
$provision_script = <<SCRIPT
  echo "\n\nmaking sure everything's up to date..."
  sudo sh -c "echo 'LC_ALL=#{$locale}\nLANG=#{$locale}' >> /etc/environment"
  sudo apt-get update
  sudo apt-get upgrade -y

  echo "\n\ninstalling dependencies..."
  sudo apt-get -y install curl git-core python-software-properties ruby-dev libpq-dev build-essential libsqlite3-0 libsqlite3-dev libxml2 libxml2-dev libxslt1-dev postgresql postgresql-contrib libreadline-dev

  echo "\n\ninstalling rbenv..."
  git clone https://github.com/rbenv/rbenv.git ~/.rbenv
  echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
  echo 'eval "$(rbenv init -)"'               >> ~/.bashrc
  source ~/.bashrc

  echo "\n\ninstalling ruby-build..."
  git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build

  echo "\n\ninstalling ruby..."
  sudo -H -u vagrant bash -i -c 'rbenv install #{$ruby_version}'
  sudo -H -u vagrant bash -i -c 'rbenv rehash'

  echo "\n\nsetting up ruby..."
  sudo -H -u vagrant bash -i -c 'rbenv global #{$ruby_version}'
  sudo -H -u vagrant bash -i -c 'gem install bundler --no-ri --no-rdoc'
  sudo -H -u vagrant bash -i -c 'rbenv rehash'

  echo "\n\nsetting up postgres..."
  sudo -u postgres createdb #{$db_name}
  echo "ALTER USER postgres WITH PASSWORD \'#{$db_password}\';" | sudo -u postgres psql
SCRIPT

# Start the config!
Vagrant.configure(2) do |config|
  # Use the ubuntu/trusty64 box (for Ubuntu 14.04 LTS).
  config.vm.box = "ubuntu/trusty64"

  # Share each port in $ports from the VM to the guest (under the same port).
  $ports.each do |port|
    config.vm.network "forwarded_port", guest: port.to_s, host: port.to_s
  end

  # Share the project directory to ~/{current-dir-name}.
  config.vm.synced_folder "./", "/home/vagrant/#{$project_name}"

  # Provider-specific settings for Virtualbox. Just setting the RAM to 1GB here.
  config.vm.provider "virtualbox" do |vb|
    # Customize the amount of memory on the VM:
    vb.memory = "1024"
  end

  # Provision the VM with the script at the top of the Vagrantfile.
  config.vm.provision :shell, privileged: false, inline: $provision_script
end