user_observer.ex

defmodule UserObserver do 
  use GenServer
  
  def start_link do
    GenServer.start_link(__MODULE__, %{}, name: __MODULE__)
  end
  
  def init(_) do
    {:ok, users} = load_users()
    timer = set_timer()
    {:ok, %{users: users, timer: timer}}
  end
  
  def handle_info(:reload, state)
    # .... Perform actions on users ....
    
    timer = set_timer()
    {:noreply, %{state | timer: timer}}
  end
  
  defp load_users do
    API.load_users()
  end
  
  defp set_timer do
    Process.send_after(self(), :reload, 10_000)
  end
end