Redirect Elixir Phoenix request from root domain to www

Question

We have a Phoenix app on Heroku with DNS at Route 53. We followed this blog post to set up the proper http to https redirect:
http://building.vts.com/blog/2015/11/02/route53-ssl-naked-domain-redirect/

Everything works and all that is remaining is redirecting the root to the subdomain www.

Is there a recommended way to set this up in a Phoenix way?

Answer 1

Simply plug in the redirect at the top of your app's endpoint.

In lib/app/endpoint.ex:

defmodule App.Endpoint do
  use Phoenix.Endpoint, otp_app: :app

  socket "/socket", App.UserSocket

  plug App.Plugs.WWWRedirect
  # ...
end

In lib/app/plugs/www_redirect.ex:

defmodule App.Plugs.WWWRedirect do
  import Plug.Conn

  def init(options) do
    options
  end

  def call(conn, _options) do
    if bare_domain?(conn.host) do
      conn
        |> Phoenix.Controller.redirect(external: www_url(conn))
        |> halt
    else
      conn # Since all plugs need to return a connection
    end
  end

  # Returns URL with www prepended for the given connection. Note this also
  # applies to hosts that already contain "www"
  defp www_url(conn) do
    "#{conn.scheme}://www.#{conn.host}"
  end

  # Returns whether the domain is bare (no www)
  defp bare_domain?(host) do
    !Regex.match?(~r/\Awww\..*\z/i, host)
  end
end

Note that you'll need to restart your sever for this to have an effect since nothing in lib is reloaded.

Answer 2

You can also use plug_canonical_host to take care of it for you and ensure that your Elixir application is only accessible through its canonical URL.