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%% This Source Code Form is subject to the terms of the Mozilla Public
%% License, v. 2.0. If a copy of the MPL was not distributed with this
%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
%%
%% Copyright (c) 2007-2021 VMware, Inc. or its affiliates. All rights reserved.
%%
-module(rabbit_epmd_monitor).
-behaviour(gen_server).
-export([start_link/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
code_change/3]).
-record(state, {timer, mod, me, host, port}).
-define(SERVER, ?MODULE).
-define(CHECK_FREQUENCY, 60000).
%%----------------------------------------------------------------------------
%% It's possible for epmd to be killed out from underneath us. If that
%% happens, then obviously clustering and rabbitmqctl stop
%% working. This process checks up on epmd and restarts it /
%% re-registers us with it if it has gone away.
%%
%% How could epmd be killed?
%%
%% 1) The most popular way for this to happen is when running as a
%% Windows service. The user starts rabbitmqctl first, and this starts
%% epmd under the user's account. When they log out epmd is killed.
%%
%% 2) Some packagings of (non-RabbitMQ?) Erlang apps might do "killall
%% epmd" as a shutdown or uninstall step.
%% ----------------------------------------------------------------------------
-spec start_link() -> rabbit_types:ok_pid_or_error().
start_link() ->
gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
init([]) ->
{Me, Host} = rabbit_nodes:parts(node()),
Mod = net_kernel:epmd_module(),
{ok, Port} = handle_port_please(init, Mod:port_please(Me, Host), Me, undefined),
State = #state{mod = Mod, me = Me, host = Host, port = Port},
{ok, ensure_timer(State)}.
handle_call(_Request, _From, State) ->
{noreply, State}.
handle_cast(check, State0) ->
{ok, State1} = check_epmd(State0),
{noreply, ensure_timer(State1#state{timer = undefined})};
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(check, State0) ->
{ok, State1} = check_epmd(State0),
{noreply, ensure_timer(State1#state{timer = undefined})};
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
%%----------------------------------------------------------------------------
ensure_timer(State) ->
rabbit_misc:ensure_timer(State, #state.timer, ?CHECK_FREQUENCY, check).
check_epmd(State = #state{mod = Mod,
me = Me,
host = Host,
port = Port0}) ->
rabbit_log:debug("Asked to [re-]register this node (~s@~s) with epmd...", [Me, Host]),
{ok, Port1} = handle_port_please(check, Mod:port_please(Me, Host), Me, Port0),
rabbit_nodes:ensure_epmd(),
Mod:register_node(Me, Port1),
rabbit_log:debug("[Re-]registered this node (~s@~s) with epmd at port ~p", [Me, Host, Port1]),
{ok, State#state{port = Port1}}.
handle_port_please(init, noport, Me, Port) ->
rabbit_log:info("epmd does not know us, re-registering as ~s~n", [Me]),
{ok, Port};
handle_port_please(check, noport, Me, Port) ->
rabbit_log:warning("epmd does not know us, re-registering ~s at port ~b~n", [Me, Port]),
{ok, Port};
handle_port_please(_, closed, _Me, Port) ->
rabbit_log:error("epmd monitor failed to retrieve our port from epmd: closed"),
{ok, Port};
handle_port_please(init, {port, NewPort, _Version}, _Me, _Port) ->
rabbit_log:info("epmd monitor knows us, inter-node communication (distribution) port: ~p", [NewPort]),
{ok, NewPort};
handle_port_please(check, {port, NewPort, _Version}, _Me, _Port) ->
{ok, NewPort};
handle_port_please(_, {error, Error}, _Me, Port) ->
rabbit_log:error("epmd monitor failed to retrieve our port from epmd: ~p", [Error]),
{ok, Port}.
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