restart_server.ex

defmodule RestartServer do
  use GenServer

  def start_link(args) do
    GenServer.start_link(__MODULE__, args, [name: __MODULE__])
  end

  def init(_) do
    IO.puts("RESTARTING")
    num = Enum.random(1..1_000_000)
    {:ok, num}
  end
end

defmodule RestartSupervisor do
  use Supervisor
  
  def start_link(args) do
    Supervisor.start_link(__MODULE__, args)
  end

  @impl true
  def init(_) do
    opts = [strategy: :one_for_one]
    Supervisor.init([{RestartServer, []}], opts)
  end
end

Process.flag(:trap_exit, true)
RestartSupervisor.start_link([])
pid = Process.whereis(RestartServer)
:sys.get_state(pid)
Process.exit(pid, :kill)
pid = Process.whereis(RestartServer)
:sys.get_state(pid)

# iex(1)> Process.flag(:trap_exit, true)
# false
# iex(2)> RestartSupervisor.start_link([])
# RESTARTING
# {:ok, #PID<0.143.0>}
# iex(3)> pid = Process.whereis(RestartServer)
# #PID<0.144.0>
# iex(4)> :sys.get_state(pid)
# 471361
# iex(5)> Process.exit(pid, :kill)
# true
# RESTARTING
# iex(6)> pid = Process.whereis(RestartServer)
# #PID<0.148.0>
# iex(7)> :sys.get_state(pid)
# 898523