I’ve set up aliases to localhost, and corresponding NameVirtualHost settings for Apache, on my Mac for each of the sites I’m developing.  Then I can just enter, for example, “myproject.local” in my browser, and view my work in progress.  (I use the nice Ruby gem “ghost” to manage aliases.)  However, this doesn’t work with a default VirtualBox guest, so below is my method for getting this to work.

Start the VirtualBox VM Manager

1. To begin, start your install of VirtualBox.  I believe that you need at least version 2.2.0, which introduced host-only networking.
   
2. Open the settings for the desired VM and navigate to the Network tab.  You should already have something in the Adapter 1 section.
   

Add a Local-Only Network Interface

1. Click on the Adapter 2 tab.  You should typically see a disabled interface, something like this:
   
2. Enable Adapter 2 by checking the box.  Then change the “Attached to:” box to “Host-only Adapter.”  The Name box shows “vboxnet0″ on my install:
   
3. Save your settings and start your virtual machine.

Verify Host-Only Adapter Address

VirtualBox should create a new network interface on your host OS that is used for host-only networking.  On Mac OS, verify this by entering the following in a Terminal:

ifconfig vboxnet0

You should see something like the following.  Note the IP address – you will need it later:

vboxnet0: flags=8943

Set up Guest OS

You need to set up host aliases in your guest OS that match those you set up in your host, only that you will point them to the IP address you noted previously.  The following instructions apply to Windows XP and newer.

1. Open your hosts file.  Use Start -> Run… and enter “notepad c:WINDOWSsystem32driversetchosts”.  UPDATE: On Windows Vista and Windows 7, there are additional protections on this file.  You will have to run Notepad (or your favorite text editor) as Administrator first – right click on its shortcut and choose “Run as administrator.”
2. Add a line to the file that associates your host-only IP address with your development site aliases.  The IP address comes first, followed by each alias, separated by spaces.

   192.168.56.1    myproject.local otherproject.local

Test the Configuration

As long as your local web server is running on the host OS, you should be able to enter one of your site aliases in the guest’s browser and get the expected results.

Prerequisites

I’m using the Ruby and RubyGems that come installed with Leopard.

You will need to install the following first:

• XCode Developer Tools
• MacPorts

Installing PostgreSQL

Install PostgreSQL from MacPorts using the following command in your Terminal:

sudo port install postgresql84 postgresql84-server

Make sure to follow the instructions printed at the end of the installation, so that you can set up PostgreSQL to start automatically.

Installing pg Gem

Update: The “pg” gem is considered the most current of those that provide a PostgreSQL access layer. I previously mentioned the “postgres” gem.

This is the part that might trip you up if you try the standard gem install pg route. There are two ways to ensure that this works.

The first is to ensure that the directory containing PostgreSQL executables (notably pg_config) is in your PATH. You can add the following to /etc/profile:

export PATH=/opt/local/lib/postgresql84/bin:$PATH

Then run sudo gem install pg as usual.

If you do not modify your PATH, use the following in your Terminal instead so that the PostgreSQL headers and libraries are found:

sudo env ARCHFLAGS="-arch i386"
  gem install pg --
  --with-pgsql-include=/opt/local/include/postgresql84
  --with-pgsql-lib=/opt/local/lib/postgresql84

Update: On Mac OS X 10.6 Snow Leopard, you may need to use “x86_64″ instead of “i386″ in the above command.

I hope that’s the full story…