For many reasons, including SEO, public-facing websites should only be available at a single domain. Many hosting providers (especially PaaS-like platforms such as Heroku and Fly.io) make apps available at a default URL. For example, Heroku apps are available at my-app-name.herokuapp.com. If those default URLs make it out into the wild, search engines might index them, resulting in indexed duplicated content. Historically, search engines have punished websites that serve duplicated content.

At Super Good, we host many Solidus apps on Heroku. Due to the nature of eCommerce, SEO is critically important to us, so we need to avoid this issue.

The ideal solution if you find yourself in this situation (or just want to avoid it) is to make your production app serve permanent redirects to the correct domain. If someone visits https://my-app-name.herokuapp.com/some/page, then they should be served a 301 redirect (“Moved Permanently”) to https://www.my-app-name.com/some/page, or whatever the desired domain happens to be.

Firstly, if you’re using a web server like NGINX as a reverse proxy in front of your application, you should use that to do the redirect and avoid load on your web application. The following options are for situations where you can’t do that because of the particulars of your hosting solution.

One option is rack-host-redirect. It’s designed for this use case, but at the time of this writing hasn’t been touched in six years. I was hesitant to add a seemingly unmaintained dependency to my app, but it’s still worth considering. There is very little code in it.

An option that doesn’t require adding a new dependency is to use built-in Rails routing features. This is a similar to aproach to what you’d do if you wanted to redirect your www traffic to a naked domain or vice versa.

Create a catch-all route that’s constrained by domain. Let’s say your app has two Heroku deployments, my-app-staging and my-app-production. You want the app to only be accessible at staging.my-app.com and www.my-app.com, and not my-app-staging.herokuapp.com and my-app-production.herokuapp.com. You could do something like this:

if Rails.env.production? || Rails.env.staging?
  match(
    "(*any)",
    to: redirect(
      domain: "my-app.com",
      subdomain: Rails.env.production? ? "www" : "staging"
    ),
    via: :all,
    constraints: {domain: "herokuapp.com"}
  )
end

The result will be that in your production and staging environments, any requests to the herokuapp.com domain (regardless of sub-domain) will be served 301 redirects to correct domain.