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.