How to find the local port a rails instance is running on?

So I would like my Rails app instances to register themselves on a "I'm up" kind of thing I'm playing with, and I'd like it to be able to mention what local port it's running on. I can't seem to find how to do it - in fact just finding out its IP is tricky and needs a bit of a hack.

But no problem, I have the IP - but how can I find what port my mongrel/thin/webrick server is running on?

To be super explicit, if I start a rails app using script/server -p 3001, what can I do to pull that 3001 inside the app.

Building on the other answers (which saved my bacon!), I expanded this to give sane fallbacks:

In development:

port = Rails::Server::Options.new.parse!(ARGV)[:Port] || 3000 rescue 3000

In all other env's:

port = Rails::Server::Options.new.parse!(ARGV)[:Port] || 80 rescue 80

The `rescue 80` covers you if you're running `rails console`. Otherwise, it raises `NameError: uninitialized constant Rails::Server`. (Maybe also early in initializers? I forget...)

The `|| 80` covers you if no -p option is given to server. Otherwise you get nil.

I played around with this a bit, and this might be the best solution for Rails 5.1:

Rails::Server::Options.new.parse!(ARGV)[:Port]

For Rails 5.1 development server.

if Rack::Server.new.options[:Port] != 9292 # rals s -p PORT
local_port = Rack::Server.new.options[:Port]
else
local_port = (ENV['PORT'] || '3000').to_i # ENV['PORT'] for foreman
end

**Two ways.**

If you're responding to a request in a controller or view, use the request object:

request.port

If you're in an initialiser and don't have access to the request object use the server options hash:

Rails::Server.new.options[:Port]

You can call `Rails::Server.new.options[:Port]` to get the port that your Rails server is running on. This will parse the `-p 3001` args from your `rails server` command, or default to port `3000`.

From inside any controller action, check the content of *request.port*, thus:


class SomeController < ApplicationController
def some_action
raise "I'm running on port #{request.port}."
end
end