Make it possible to pre-configure cluster name via config

Per discussion with @gerhard.

Author: michaelklishin

priv/schema/rabbit.schema

@@ -383,14 +383,20 @@ end}.
     {datatype, {enum, [distinguished_name, common_name]}}
 ]}.
 
-%% SSL handshake timeout, in milliseconds.
+%% TLS handshake timeout, in milliseconds.
 %%
 %% {ssl_handshake_timeout, 5000},
 
 {mapping, "ssl_handshake_timeout", "rabbit.ssl_handshake_timeout", [
     {datatype, integer}
 ]}.
 
+%% Cluster name
+
+{mapping, "cluster_name", "rabbit.cluster_name", [
+    {datatype, string}
+]}.
+
 %% Default worker process pool size. Used to limit maximum concurrency rate
 %% of certain operations, e.g. queue initialisation and recovery on node boot.
 

src/rabbit.erl

@@ -226,6 +226,12 @@
                    [{description, "ready to communicate with peers and clients"},
                     {requires,    [core_initialized, recovery, routing_ready]}]}).
 
+-rabbit_boot_step({cluster_name,
+                   [{description, "sets cluster name if configured"},
+                    {mfa,         {rabbit_nodes, boot, []}},
+                    {requires,    pre_flight}
+                    ]}).
+
 -rabbit_boot_step({direct_client,
                    [{description, "direct client"},
                     {mfa,         {rabbit_direct, boot, []}},

src/rabbit_nodes.erl

@@ -19,18 +19,28 @@
 
 -export([names/1, diagnostics/1, make/1, parts/1, cookie_hash/0,
          is_running/2, is_process_running/2,
-         cluster_name/0, set_cluster_name/2, ensure_epmd/0,
+         cluster_name/0, set_cluster_name/1, set_cluster_name/2, ensure_epmd/0,
          all_running/0, name_type/0, running_count/0,
-         await_running_count/2]).
+         await_running_count/2,
+         boot/0]).
 
 -include_lib("kernel/include/inet.hrl").
+-include_lib("rabbit_common/include/rabbit.hrl").
 
 -define(SAMPLING_INTERVAL, 1000).
 
 %%----------------------------------------------------------------------------
-%% Specs
+%% API
 %%----------------------------------------------------------------------------
 
+boot() ->
+  case application:get_env(rabbit, cluster_name) of
+    undefined  -> ok;
+    {ok, Name} ->
+      rabbit_log:info("Setting cluster name to '~s' as configured", [Name]),
+      set_cluster_name(rabbit_data_coercion:to_binary(Name))
+  end.
+
 name_type() ->
     case os:getenv("RABBITMQ_USE_LONGNAME") of
         "true" -> longnames;
@@ -80,6 +90,11 @@ cluster_name_default() ->
     FQDN = rabbit_net:hostname(),
     list_to_binary(atom_to_list(make({ID, FQDN}))).
 
+-spec set_cluster_name(binary()) -> 'ok'.
+
+set_cluster_name(Name) ->
+    set_cluster_name(Name, ?INTERNAL_USER).
+
 -spec set_cluster_name(binary(), rabbit_types:username()) -> 'ok'.
 
 set_cluster_name(Name, Username) ->