would a simple script executed by foreman user would suffice?

at the moment, since there are is no background processing in foreman, the request would block the UI (e.g. the UI would wait until the script would finish)

Seems fine to me. Would be nice if Foreman could capture stdout/stderr and/or warn the user on a non-0 exit of the script.

would you like to get a notice in the UI / email ?

who should be noticed? the owner of the host? the creator of the host?

I think notification through the UI is a reasonable starting place.

following a discussion on irc
here is an example http://pastie.org/3888211

I would like to see something like this to have foreman update freeipa upon host creation

You can implement hooking into host creation/deletion by writing a Foreman Plugin - http://theforeman.org/projects/foreman/wiki/Plugins

Just follow the example at http://theforeman.org/projects/foreman/wiki/How_to_Create_a_Plugin

https://github.com/isratrade/foreman_plugin_template/blob/master/app/models/foreman_plugin_template/host_extensions.rb

module HostExtensions
  extend ActiveSupport::Concern

  included do
    execute standard callbacks
    after_create :do_this
    after_destroy :do_that

    execute custom hooks
    after_ready_for_build :do_something_special_after_build
    def do_something_special_after_build
      p "doing customized callback something special AFTER build" 
    end
  end
end