Start ExSync manually to ensure it's started if (and only if) Relive

mix.exs

@@ -165,7 +165,7 @@ defmodule Ejabberd.MixProject do
  {Mix.env() == :translations,
  {:ejabberd_po, git: "https://github.com/processone/ejabberd-po.git"}},
  {Mix.env() == :dev,
- {:exsync, "~> 0.2"}},
+ {:exsync, "~> 0.2", optional: true, runtime: false}},
  {config(:redis), {:eredis, "~> 1.2.0"}},
  {config(:sip), {:esip, "~> 1.0"}},
  {config(:zlib), {:ezlib, "~> 1.0"}},
@@ -183,7 +183,6 @@ defmodule Ejabberd.MixProject do
 
  defp cond_apps do
  for {:true, app} <- [{config(:stun), :stun},
- {Map.has_key?(System.get_env(), "RELIVE"), :exsync},
  {if_version_below(~c"27", true), :jiffy},
  {config(:tools), :observer}], do:
  app

src/ejabberd_app.erl

@@ -59,6 +59,7 @@ start(normal, _Args) ->
  ejabberd_hooks:run(ejabberd_started, []),
  ejabberd:check_apps(),
  ejabberd_systemd:ready(),
+ maybe_start_exsync(),
  {T2, _} = statistics(wall_clock),
  ?INFO_MSG("ejabberd ~ts is started in the node ~p in ~.2fs",
  [ejabberd_option:version(),
@@ -198,8 +199,15 @@ start_elixir_application() ->
  ok -> ok;
  {error, _Msg} -> ?ERROR_MSG("Elixir application not started.", [])
  end.
+
+maybe_start_exsync() ->
+ case os:getenv("RELIVE") of
+ "true" -> rpc:call(node(), 'Elixir.ExSync.Application', start, []);
+ _ -> ok
+ end.
 -else.
 setup_if_elixir_conf_used() -> ok.
 register_elixir_config_hooks() -> ok.
 start_elixir_application() -> ok.
+maybe_start_exsync() -> ok.
 -endif.