feat: add API to disable/enable auto clustering

The API can be used to prevent a node from re-joining the same cluster after it has (manually) left the cluster.

src/ekka.erl

@@ -38,6 +38,9 @@
 %% Autocluster API
 -export([ autocluster/0
         , autocluster/1
+        , autocluster_enabled/0
+        , enable_autocluster/0
+        , disable_autocluster/0
         ]).
 
 %% Callbacks
@@ -169,6 +172,18 @@ autocluster(App) ->
         false -> ok
     end.
 
+autocluster_enabled() ->
+    env(cluster_enable, true) andalso ekka_autocluster:configured().
+
+disable_autocluster() ->
+    ok = application:set_env(ekka, cluster_enable, false),
+    ok = mria:disable_core_node_discovery(),
+    ok = ekka_autocluster:stop(disabled).
+
+enable_autocluster() ->
+    ok = application:set_env(ekka, cluster_enable, true),
+    ok = mria:enable_core_node_discovery().
+
 %%--------------------------------------------------------------------
 %% Callbacks
 %%--------------------------------------------------------------------

src/ekka_autocluster.erl

@@ -23,9 +23,11 @@
 
 %% API
 -export([ enabled/0
+        , configured/0
         , run/1
         , unregister_node/0
         , core_node_discovery_callback/0
+        , stop/1
         ]).
 
 %% gen_server callbacks
@@ -49,9 +51,13 @@
 
 -spec enabled() -> boolean().
 enabled() ->
+    configured() andalso mria_config:role() =:= core.
+
+-spec configured() -> boolean().
+configured() ->
     case ekka:env(cluster_discovery) of
         {ok, {manual, _}} -> false;
-        {ok, _Strategy}   -> mria_config:role() =:= core;
+        {ok, _Strategy}   -> true;
         undefined         -> false
     end.
 
@@ -74,6 +80,15 @@ unregister_node() ->
           log_error("Unregister", ekka_cluster_strategy:unregister(Mod, Options))
       end).
 
+-spec stop(term()) -> ok.
+stop(Reason) ->
+    try
+        gen_server:stop(?SERVER, {shutdown, Reason}, 5000)
+    catch
+        _:noproc ->
+            ok
+    end.
+
 %% @doc Core node discovery used by mria by replicant nodes to find
 %% the core nodes.
 -spec core_node_discovery_callback() -> [node()].