From c3391bb822f0516975b293bc220e1a44cdb8bc0c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Valim?= <jose.valim@plataformatec.com.br>
Date: Wed, 9 Jan 2019 12:24:17 +0100
Subject: Add start_distribution to kernel environment

Sometimes you may want to start Erlang without any
of its distribution services. This commit adds an
environment configuration that allows so.

Because the servers we don't start here are a subset
of the servers not started on minimal mode, we do
have a guarantee that the system can still operate
as the system operates without those apps on minimal
mode.
---
 lib/kernel/src/kernel.erl | 72 ++++++++++++++++++++++++++---------------------
 1 file changed, 40 insertions(+), 32 deletions(-)

(limited to 'lib/kernel/src/kernel.erl')

diff --git a/lib/kernel/src/kernel.erl b/lib/kernel/src/kernel.erl
index c68d04e279..111d103df2 100644
--- a/lib/kernel/src/kernel.erl
+++ b/lib/kernel/src/kernel.erl
@@ -145,26 +145,11 @@ init([]) ->
             {ok, {SupFlags,
                   [Code, File, StdError, User, LoggerSup, Config, RefC, SafeSup]}};
         _ ->
-            Rpc = #{id => rex,
-                    start => {rpc, start_link, []},
-                    restart => permanent,
-                    shutdown => 2000,
-                    type => worker,
-                    modules => [rpc]},
-
-            Global = #{id => global_name_server,
-                       start => {global, start_link, []},
-                       restart => permanent,
-                       shutdown => 2000,
-                       type => worker,
-                       modules => [global]},
-
-            GlGroup = #{id => global_group,
-                        start => {global_group,start_link,[]},
-                        restart => permanent,
-                        shutdown => 2000,
-                        type => worker,
-                        modules => [global_group]},
+            DistChildren =
+		case application:get_env(kernel, start_distribution) of
+		    {ok, false} -> [];
+		    _ -> start_distribution()
+		end,
 
             InetDb = #{id => inet_db,
                        start => {inet_db, start_link, []},
@@ -173,13 +158,6 @@ init([]) ->
                        type => worker,
                        modules => [inet_db]},
 
-            NetSup = #{id => net_sup,
-                       start => {erl_distribution, start_link, []},
-                       restart => permanent,
-                       shutdown => infinity,
-                       type => supervisor,
-                       modules => [erl_distribution]},
-
             SigSrv = #{id => erl_signal_server,
                        start => {gen_event, start_link, [{local, erl_signal_server}]},
                        restart => permanent,
@@ -187,14 +165,11 @@ init([]) ->
                        type => worker,
                        modules => dynamic},
 
-            DistAC = start_dist_ac(),
-
             Timer = start_timer(),
 
             {ok, {SupFlags,
-                  [Code, Rpc, Global, InetDb | DistAC] ++
-                  [NetSup, GlGroup, File, SigSrv,
-                   StdError, User, Config, RefC, SafeSup, LoggerSup] ++ Timer}}
+                  [Code, InetDb | DistChildren] ++
+                  [File, SigSrv, StdError, User, Config, RefC, SafeSup, LoggerSup] ++ Timer}}
     end;
 init(safe) ->
     SupFlags = #{strategy => one_for_one,
@@ -213,6 +188,39 @@ init(safe) ->
 
     {ok, {SupFlags, Boot ++ DiskLog ++ Pg2}}.
 
+start_distribution() ->
+    Rpc = #{id => rex,
+            start => {rpc, start_link, []},
+            restart => permanent,
+            shutdown => 2000,
+            type => worker,
+            modules => [rpc]},
+
+    Global = #{id => global_name_server,
+               start => {global, start_link, []},
+               restart => permanent,
+               shutdown => 2000,
+               type => worker,
+               modules => [global]},
+
+    DistAC = start_dist_ac(),
+
+    NetSup = #{id => net_sup,
+               start => {erl_distribution, start_link, []},
+               restart => permanent,
+               shutdown => infinity,
+               type => supervisor,
+               modules => [erl_distribution]},
+
+    GlGroup = #{id => global_group,
+                start => {global_group,start_link,[]},
+                restart => permanent,
+                shutdown => 2000,
+                type => worker,
+                modules => [global_group]},
+
+    [Rpc, Global | DistAC] ++ [NetSup, GlGroup].
+
 start_dist_ac() ->
     Spec = [#{id => dist_ac,
               start => {dist_ac,start_link,[]},
-- 
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