networking - Getting the Hostname or IP in Ruby on Rails

Question

I'm in the process of maintaining a Ruby on Rails app and am looking for an easy way to find the hostname or IP address of the box I'm on (since it's a VM and new instances may have different hostnames or IP addresses). Is there a quick and easy way to do this in Ruby on Rails?

Edit: The answer below is correct but the clarification Craig provided is useful (see also provided link in answer):

The [below] code does NOT make a connection or send any packets (to 64.233.187.99 which is google). Since UDP is a stateless protocol connect() merely makes a system call which figures out how to route the packets based on the address and what interface (and therefore IP address) it should bind to. addr() returns an array containing the family (AF_INET), local port, and local address (which is what we want) of the socket.

Answer 1

Hostname

A simple way to just get the hostname in Ruby is:

require 'socket'
hostname = Socket.gethostname

The catch is that this relies on the host knowing its own name because it uses either the gethostname or uname system call, so it will not work for the original problem.

Functionally this is identical to the hostname answer, without invoking an external program. The hostname may or may not be fully qualified, depending on the machine's configuration.

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IP Address

Since ruby 1.9, you can also use the Socket library to get a list of local addresses. ip_address_list returns an array of AddrInfo objects. How you choose from it will depend on what you want to do and how many interfaces you have, but here's an example which simply selects the first non-loopback IPV4 IP address as a string:

require 'socket'
ip_address = Socket.ip_address_list.find { |ai| ai.ipv4? && !ai.ipv4_loopback? }.ip_address