feat: add singleton strategy

emqx · Jun 13, 2024 · 41618f3 · 41618f3
1 parent cd2877b
commit 41618f3
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Showing 3 changed files with 60 additions and 1 deletion.
diff --git a/src/ekka_autocluster.erl b/src/ekka_autocluster.erl
@@ -57,6 +57,7 @@ enabled() ->
 configured() ->
     case ekka:env(cluster_discovery) of
         {ok, {manual, _}} -> false;
+        {ok, {singleton, _}} -> false;
         {ok, _Strategy}   -> true;
         undefined         -> false
     end.
@@ -96,6 +97,8 @@ core_node_discovery_callback() ->
     case ekka:env(cluster_discovery) of
         {ok, {manual, _}} ->
             [];
+        {ok, {singleton, _}} ->
+            [];
         {ok, {Strategy, Options}} ->
             Mod = strategy_module(Strategy),
             try ekka_cluster_strategy:discover(Mod, Options) of
@@ -197,6 +200,8 @@ with_strategy(Fun) ->
     case ekka:env(cluster_discovery) of
         {ok, {manual, _}} ->
             ignore;
+        {ok, {singleton, _}} ->
+            ignore;
         {ok, {Strategy, Options}} ->
             Fun(strategy_module(Strategy), Options);
         undefined ->

diff --git a/src/ekka_cluster.erl b/src/ekka_cluster.erl
@@ -24,6 +24,8 @@
         , leave/0
         , force_leave/1
         , status/1
+        , is_singleton/0
+        , is_singleton/1
         ]).
 
 -type(info_key() :: running_nodes | stopped_nodes).
@@ -50,7 +52,12 @@ status(Node) ->
 %% @doc Join the cluster
 -spec(join(node()) -> ok | ignore | {error, term()}).
 join(Node) ->
-    mria:join(Node).
+    case is_singleton() orelse is_singleton(Node) of
+        true ->
+            {error, singleton};
+        false ->
+            mria:join(Node)
+    end.
 
 %% @doc Leave from the cluster.
 -spec(leave() -> ok | {error, any()}).
@@ -61,3 +68,23 @@ leave() ->
 -spec(force_leave(node()) -> ok | ignore | {error, term()}).
 force_leave(Node) ->
     mria:force_leave(Node).
+
+-spec is_singleton() -> boolean().
+is_singleton() ->
+    case ekka:env(cluster_discovery) of
+        {ok, {singleton, _}} ->
+            true;
+        _ ->
+            false
+    end.
+
+-spec is_singleton(node()) -> boolean().
+is_singleton(Node) when Node =:= node() ->
+    is_singleton();
+is_singleton(Node) ->
+    try
+        erpc:call(Node, ?MODULE, is_singleton, [])
+    catch
+        _:_ ->
+            false
+    end.
diff --git a/test/ekka_autocluster_SUITE.erl b/test/ekka_autocluster_SUITE.erl
@@ -41,6 +41,8 @@
                       {suffix, ""}
                      ]).
 
+-define(ON(NODE, BODY), erpc:call(NODE, fun() -> BODY end)).
+
 all() -> ekka_ct:all(?MODULE).
 
 %%--------------------------------------------------------------------
@@ -330,6 +332,31 @@ t_core_node_discovery_callback(Config) ->
       ),
     ok.
 
+%%--------------------------------------------------------------------
+%% "Autocluster" via 'singleton' strategy
+
+t_singleton(_Config) ->
+    N1 = ekka_ct:start_slave(ekka, n1),
+    N2 = ekka_ct:start_slave(ekka, n2),
+    try
+        ok = ekka_ct:wait_running(N1),
+        ok = ekka_ct:wait_running(N2),
+        ok = set_app_env(N1, {singleton, []}),
+        ok = set_app_env(N2, {static, [{seeds, []}]}),
+        ?ON(N1, ?assertMatch({error, singleton}, ekka:join(N2))),
+        %% Other nodes must not join the singleton.
+        ?ON(N2, ?assertMatch({error, singleton}, ekka:join(N1))),
+        ?ON(N1, ?assertNot(ekka:autocluster_enabled())),
+        ?ON(N1, ?assertNot(ekka_autocluster:configured())),
+        ?ON(N1, ?assertNot(ekka_autocluster:enabled())),
+        ?ON(N1, ?assertEqual(ignore, ekka_autocluster:run(myapp))),
+        ?ON(N1, ?assertEqual(ignore, ekka_autocluster:unregister_node())),
+        ?ON(N1, ?assertEqual([], ekka_autocluster:core_node_discovery_callback())),
+        ok
+    after
+        ok = ekka_ct:stop_slave(N1)
+    end.
+
 %%--------------------------------------------------------------------
 %% Misc tests
 %%--------------------------------------------------------------------