I wanted to use url_for in a job, so I added the following:

# Routes aren't included by default into job classes so it's up to the developer to configure what they need
# When the module is included we'll add a class attribute if there's no existing default_url_options method.
# Where we do include them by default we have config options - one for Action Mailer and one for Action Controller.
# taken from: https://github.com/rails/rails/issues/29992#issuecomment-318819265
include Rails.application.routes.url_helpers
  def default_url_options

So in the above code I tell the job to use the ActionMailer default_url_options which is:

config.action_mailer.default_url_options = { :host => "http://www.mysite.io" }

Now when my job runs it tries to open the report at https://www.mysite.io/rails/active_storage/blobs/crazyguid/report.pdf