refactor(emqx): ensure app shutdown and reboot order

make use of application dependency to ensure start order.
also the same dependency top-sorted for shutdown and reboot order

.ci/docker-compose-file/conf.cluster.env

@@ -6,8 +6,3 @@ EMQX_ZONES__DEFAULT__LISTENERS__MQTT_WS__PROXY_PROTOCOL=true
 EMQX_LOG__CONSOLE_HANDLER__ENABLE=true
 EMQX_LOG__CONSOLE_HANDLER__LEVEL=debug
 EMQX_LOG__PRIMARY_LEVEL=debug
-EMQX_ZONES__DEFAULT__MQTT__MAX_TOPIC_ALIAS=10
-EMQX_ZONES__DEFAULT__MQTT__RETRY_INTERVAL=2s
-HOCON_ENV_OVERRIDE_PREFIX=EMQX_
-EMQX_LOG__PRIMARY_LEVEL=debug
-EMQX_LOG__CONSOLE_HANDLER__LEVEL=debug

apps/emqx/src/emqx.erl

@@ -23,7 +23,6 @@
 
 %% Start/Stop the application
 -export([ start/0
-        , restart/1
         , is_running/1
         , stop/0
         ]).
@@ -52,12 +51,6 @@
         , run_fold_hook/3
         ]).
 
-%% Shutdown and reboot
--export([ shutdown/0
-        , shutdown/1
-        , reboot/0
-        ]).
-
 %% Troubleshooting
 -export([ set_debug_secret/1
         ]).
@@ -94,19 +87,8 @@ set_debug_secret(PathToSecretFile) ->
 %% @doc Start emqx application
 -spec(start() -> {ok, list(atom())} | {error, term()}).
 start() ->
-    %% Check OS
-    %% Check VM
-    %% Check Mnesia
     application:ensure_all_started(?APP).
 
--spec(restart(string()) -> ok).
-restart(ConfFile) ->
-    reload_config(ConfFile),
-    shutdown(),
-    ok = application:stop(mnesia),
-    _ = application:start(mnesia),
-    reboot().
-
 %% @doc Stop emqx application.
 -spec(stop() -> ok | {error, term()}).
 stop() ->
@@ -202,43 +184,3 @@ run_hook(HookPoint, Args) ->
 -spec(run_fold_hook(emqx_hooks:hookpoint(), list(any()), any()) -> any()).
 run_fold_hook(HookPoint, Args, Acc) ->
     emqx_hooks:run_fold(HookPoint, Args, Acc).
-
-%%--------------------------------------------------------------------
-%% Shutdown and reboot
-%%--------------------------------------------------------------------
-
-shutdown() ->
-    shutdown(normal).
-
-shutdown(Reason) ->
-    ?SLOG(critical, #{msg => "stopping_apps", reason => Reason}),
-    _ = emqx_alarm_handler:unload(),
-    lists:foreach(fun stop_app/1, lists:reverse(default_started_applications())).
-
-
-stop_app(App) ->
-    ?SLOG(debug, #{msg => "stopping_app", app => App}),
-    application:stop(App).
-
-reboot() ->
-    lists:foreach(fun application:start/1 , default_started_applications()).
-
-default_started_applications() ->
-    [gproc, esockd, ranch, cowboy, ekka, quicer, emqx] ++ emqx_feature().
-
-%%--------------------------------------------------------------------
-%% Internal functions
-%%--------------------------------------------------------------------
-
-reload_config(ConfFile) ->
-    {ok, [Conf]} = file:consult(ConfFile),
-    lists:foreach(fun({App, Vals}) ->
-                      [application:set_env(App, Par, Val) || {Par, Val} <- Vals]
-                  end, Conf).
-
--ifndef(EMQX_DEP_APPS).
-emqx_feature() -> [].
--else.
-emqx_feature() ->
-    ?EMQX_DEP_APPS.
--endif.

apps/emqx/src/emqx_app.erl

@@ -53,7 +53,6 @@ start(_Type, _Args) ->
     ok = maybe_start_quicer(),
     {ok, Sup} = emqx_sup:start_link(),
     ok = maybe_start_listeners(),
-    ok = start_autocluster(),
     ok = emqx_alarm_handler:load(),
     register(emqx, self()),
     {ok, Sup}.
@@ -132,9 +131,3 @@ get_release() ->
 
 release_in_macro() ->
     element(2, ?EMQX_RELEASE).
-
-start_autocluster() ->
-    ekka:callback(prepare, fun emqx:shutdown/1),
-    ekka:callback(reboot,  fun emqx:reboot/0),
-    _ = ekka:autocluster(?APP), %% returns 'ok' or a pid or 'any()' as in spec
-    ok.

apps/emqx/test/emqx_SUITE.erl

@@ -32,25 +32,6 @@ init_per_suite(Config) ->
 end_per_suite(_Config) ->
     emqx_ct_helpers:stop_apps([]).
 
-t_restart(_) ->
-    ConfFile = "test.config",
-    Data = "[{emqx_statsd,[{interval,15000},{push_gateway,\"http://127.0.0.1:9091\"}]}].",
-    file:write_file(ConfFile, list_to_binary(Data)),
-    emqx:restart(ConfFile),
-    file:delete(ConfFile).
-
-t_stop_start(_) ->
-    emqx:stop(),
-    false = emqx:is_running(node()),
-    emqx:start(),
-    true = emqx:is_running(node()),
-    ok = emqx:shutdown(),
-    false = emqx:is_running(node()),
-    ok = emqx:reboot(),
-    true = emqx:is_running(node()),
-    ok = emqx:shutdown(for_test),
-    false = emqx:is_running(node()).
-
 t_emqx_pubsub_api(_) ->
     true = emqx:is_running(node()),
     {ok, C} = emqtt:start_link([{host, "localhost"}, {clientid, "myclient"}]),

apps/emqx_bridge_mqtt/src/emqx_bridge_mqtt.app.src

@@ -3,7 +3,7 @@
   {vsn, "5.0.0"}, % strict semver, bump manually!
   {modules, []},
   {registered, []},
-  {applications, [kernel,stdlib,replayq,emqtt]},
+  {applications, [kernel,stdlib,replayq,emqtt,emqx]},
   {mod, {emqx_bridge_mqtt_app, []}},
   {env, []},
   {licenses, ["Apache-2.0"]},

apps/emqx_connector/src/emqx_connector.app.src

@@ -12,7 +12,8 @@
     eredis,
     epgsql,
     mysql,
-    mongodb
+    mongodb,
+    emqx
    ]},
   {env,[]},
   {modules, []},

apps/emqx_dashboard/src/emqx_dashboard.app.src

@@ -3,7 +3,7 @@
   {vsn, "5.0.0"}, % strict semver, bump manually!
   {modules, []},
   {registered, [emqx_dashboard_sup]},
-  {applications, [kernel,stdlib,mnesia,minirest]},
+  {applications, [kernel,stdlib,mnesia,minirest,emqx]},
   {mod, {emqx_dashboard_app,[]}},
   {env, []},
   {licenses, ["Apache-2.0"]},

apps/emqx_data_bridge/src/emqx_data_bridge.app.src

@@ -5,7 +5,8 @@
   {mod, {emqx_data_bridge_app, []}},
   {applications,
    [kernel,
-    stdlib
+    stdlib,
+    emqx
    ]},
   {env,[]},
   {modules, []},

apps/emqx_exhook/src/emqx_exhook.app.src

@@ -4,7 +4,7 @@
   {modules, []},
   {registered, []},
   {mod, {emqx_exhook_app, []}},
-  {applications, [kernel,stdlib,grpc]},
+  {applications, [kernel,stdlib,grpc,emqx]},
   {env,[]},
   {licenses, ["Apache-2.0"]},
   {maintainers, ["EMQ X Team <contact@emqx.io>"]},

apps/emqx_gateway/src/emqx_gateway.app.src

@@ -3,7 +3,7 @@
   {vsn, "0.1.0"},
   {registered, []},
   {mod, {emqx_gateway_app, []}},
-  {applications, [kernel, stdlib, grpc, lwm2m_coap]},
+  {applications, [kernel, stdlib, grpc, lwm2m_coap, emqx]},
   {env, []},
   {modules, []},
   {licenses, ["Apache 2.0"]},

apps/emqx_machine/src/emqx_machine_app.erl

@@ -21,6 +21,13 @@
         , prep_stop/1
         ]).
 
+%% Shutdown and reboot
+-export([ shutdown/1
+        , ensure_apps_started/0
+        ]).
+
+-export([sorted_reboot_apps/0]).
+
 -behaviour(application).
 
 -include_lib("emqx/include/logger.hrl").
@@ -28,18 +35,21 @@
 start(_Type, _Args) ->
     ok = set_backtrace_depth(),
     ok = print_otp_version_warning(),
-    _ = load_modules(),
 
+    %% need to load some app envs
+    %% TODO delete it once emqx boot does not depend on modules envs
+    _ = load_modules(),
     ok = load_config_files(),
 
     {ok, RootSupPid} = emqx_machine_sup:start_link(),
 
-    {ok, _} = application:ensure_all_started(emqx),
+    ok = ensure_apps_started(),
 
     _ = emqx_plugins:load(),
-    _ = start_modules(),
 
     ok = print_vsn(),
+
+    ok = start_autocluster(),
     {ok, RootSupPid}.
 
 prep_stop(_State) ->
@@ -71,13 +81,9 @@ print_vsn() ->
 -ifndef(EMQX_ENTERPRISE).
 load_modules() ->
     application:load(emqx_modules).
-start_modules() ->
-    application:ensure_all_started(emqx_modules).
 -else.
 load_modules() ->
     ok.
-start_modules() ->
-    ok.
 -endif.
 
 load_config_files() ->
@@ -88,3 +94,83 @@ load_config_files() ->
     ok = emqx_config:init_load(emqx_machine_schema, ConfFiles),
     %% to avoid config being loaded again when emqx app starts.
     ok = emqx_app:set_init_config_load_done().
+
+start_autocluster() ->
+    ekka:callback(prepare, fun ?MODULE:shutdown/1),
+    ekka:callback(reboot,  fun ?MODULE:ensure_apps_started/0),
+    _ = ekka:autocluster(emqx), %% returns 'ok' or a pid or 'any()' as in spec
+    ok.
+
+shutdown(Reason) ->
+    ?SLOG(critical, #{msg => "stopping_apps", reason => Reason}),
+    _ = emqx_alarm_handler:unload(),
+    lists:foreach(fun stop_one_app/1, lists:reverse(sorted_reboot_apps())).
+
+stop_one_app(App) ->
+    ?SLOG(debug, #{msg => "stopping_app", app => App}),
+    application:stop(App).
+
+ensure_apps_started() ->
+    lists:foreach(fun start_one_app/1, sorted_reboot_apps()).
+
+start_one_app(App) ->
+    ?SLOG(debug, #{msg => "starting_app", app => App}),
+    case application:ensure_all_started(App) of
+        {ok, Apps} ->
+            ?SLOG(debug, #{msg => "started_apps", apps => [App | Apps]});
+        {error, Reason} ->
+            ?SLOG(critical, #{msg => "failed_to_start_app", app => App, reason => Reason}),
+            error({faile_to_start_app, App, Reason})
+    end.
+
+%% list of app names which should be rebooted when:
+%% 1. due to static static config change
+%% 2. after join a cluster
+reboot_apps() ->
+    [gproc, esockd, ranch, cowboy, ekka, quicer, emqx | ?EMQX_DEP_APPS].
+
+%% quicer can not be added to emqx's .app because it might be opted out at build time
+implicit_deps() ->
+    [{emqx, [quicer]}].
+
+sorted_reboot_apps() ->
+    Apps = [{App, app_deps(App)} || App <- reboot_apps()],
+    sorted_reboot_apps(Apps ++ implicit_deps()).
+
+app_deps(App) ->
+    case application:get_key(App, applications) of
+        undefined -> [];
+        {ok, List} -> lists:filter(fun(A) -> lists:member(A, reboot_apps()) end, List)
+    end.
+
+sorted_reboot_apps(Apps) ->
+    G = digraph:new(),
+    lists:foreach(fun({App, Deps}) -> add_app(G, App, Deps) end, Apps),
+    case digraph_utils:topsort(G) of
+        Sorted when is_list(Sorted) ->
+            Sorted;
+        false ->
+            Loops = find_loops(G),
+            error({circular_application_dependency, Loops})
+    end.
+
+add_app(G, App, undefined) ->
+    ?SLOG(debug, #{msg => "app_is_not_loaded", app => App}),
+    %% not loaded
+    add_app(G, App, []);
+add_app(_G, _App, []) ->
+    ok;
+add_app(G, App, [Dep | Deps]) ->
+    digraph:add_vertex(G, App),
+    digraph:add_vertex(G, Dep),
+    digraph:add_edge(G, Dep, App), %% dep -> app as dependency
+    add_app(G, App, Deps).
+
+find_loops(G) ->
+    lists:filtermap(
+      fun (App) ->
+              case digraph:get_short_cycle(G, App) of
+                  false -> false;
+                  Apps -> {true, Apps}
+              end
+      end, digraph:vertices(G)).

apps/emqx_machine/src/emqx_machine_sup.erl

@@ -14,6 +14,8 @@
 %% limitations under the License.
 %%--------------------------------------------------------------------
 
+%% @doc This supervisor manages workers which should never need a restart
+%% due to config changes or when joining a cluster.
 -module(emqx_machine_sup).
 
 -behaviour(supervisor).
@@ -35,15 +37,6 @@ init([]) ->
                 },
     {ok, {SupFlags, Children}}.
 
-% child_supervisor(Mod) ->
-%     #{id => Mod,
-%       start => {Mod, start_link, []},
-%       restart => permanent,
-%       shutdown => infinity,
-%       type => supervisor,
-%       modules => [Mod]
-%      }.
-
 child_worker(M, Args) ->
     #{id       => M,
       start    => {M, start_link, Args},

apps/emqx_machine/test/emqx_machine_app_SUITE.erl

@@ -0,0 +1,41 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2020-2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+
+-module(emqx_machine_app_SUITE).
+
+-compile(export_all).
+-compile(nowarn_export_all).
+
+-include_lib("emqx/include/emqx.hrl").
+-include_lib("eunit/include/eunit.hrl").
+-include_lib("common_test/include/ct.hrl").
+
+all() -> emqx_ct:all(?MODULE).
+
+init_per_suite(Config) ->
+    emqx_ct_helpers:start_apps([]),
+    Config.
+
+end_per_suite(_Config) ->
+    emqx_ct_helpers:stop_apps([]).
+
+t_shutdown_reboot(_Config) ->
+    emqx_machine_app:shutdown(normal),
+    false = emqx:is_running(node()),
+    emqx_machine_app:ensure_apps_started(),
+    true = emqx:is_running(node()),
+    ok = emqx_machine_app:shutdown(for_test),
+    false = emqx:is_running(node()).

apps/emqx_management/src/emqx_management.app.src

@@ -3,7 +3,7 @@
   {vsn, "5.0.0"}, % strict semver, bump manually!
   {modules, []},
   {registered, [emqx_management_sup]},
-  {applications, [kernel,stdlib,minirest]},
+  {applications, [kernel,stdlib,minirest,emqx]},
   {mod, {emqx_mgmt_app,[]}},
   {env, []},
   {licenses, ["Apache-2.0"]},

apps/emqx_modules/src/emqx_modules.app.src

@@ -2,7 +2,7 @@
  [{description, "EMQ X Modules"},
   {vsn, "5.0.0"},
   {modules, []},
-  {applications, [kernel,stdlib]},
+  {applications, [kernel,stdlib,emqx]},
   {mod, {emqx_modules_app, []}},
   {registered, [emqx_modules_sup]},
   {env, []}

apps/emqx_prometheus/src/emqx_prometheus.app.src

@@ -3,7 +3,7 @@
   {vsn, "5.0.0"}, % strict semver, bump manually!
   {modules, []},
   {registered, [emqx_prometheus_sup]},
-  {applications, [kernel,stdlib,prometheus]},
+  {applications, [kernel,stdlib,prometheus,emqx]},
   {mod, {emqx_prometheus_app,[]}},
   {env, []},
   {licenses, ["Apache-2.0"]},

apps/emqx_resource/src/emqx_resource.app.src

@@ -8,7 +8,8 @@
     stdlib,
     gproc,
     hocon,
-    jsx
+    jsx,
+    emqx
    ]},
   {env,[]},
   {modules, []},

apps/emqx_retainer/src/emqx_retainer.app.src

@@ -3,7 +3,7 @@
   {vsn, "5.0.0"}, % strict semver, bump manually!
   {modules, []},
   {registered, [emqx_retainer_sup]},
-  {applications, [kernel,stdlib]},
+  {applications, [kernel,stdlib,emqx]},
   {mod, {emqx_retainer_app,[]}},
   {env, []},
   {licenses, ["Apache-2.0"]},

apps/emqx_rule_actions/src/emqx_rule_actions.app.src

@@ -3,7 +3,7 @@
   {vsn, "5.0.0"},
   {registered, []},
   {applications,
-   [kernel,stdlib]},
+   [kernel,stdlib,emqx]},
   {env,[]},
   {modules, []},
   {licenses, ["Apache 2.0"]},

apps/emqx_statsd/src/emqx_statsd.app.src

@@ -6,7 +6,8 @@
   {applications,
    [kernel,
     stdlib,
-    estatsd
+    estatsd,
+    emqx
    ]},
   {env,[]},
   {modules, []},

rebar.config.erl

@@ -458,8 +458,13 @@ coveralls() ->
 app_names() -> list_dir("apps") ++ list_dir("lib-ee").
 
 list_dir(Dir) ->
-    {ok, Names} = file:list_dir(Dir),
-    [list_to_atom(Name) || Name <- Names, filelib:is_dir(filename:join([Dir, Name]))].
+    case filelib:is_dir(Dir) of
+        true ->
+            {ok, Names} = file:list_dir(Dir),
+            [list_to_atom(Name) || Name <- Names, filelib:is_dir(filename:join([Dir, Name]))];
+        false ->
+            []
+    end.
 
 %% ==== Enterprise supports below ==================================================================