Add an 'is-in-service' health check wrapping rabbit:is_serving/0

This is useful for a load balancer, for example, to be able to avoid
sending new connections to a node which is running and has listeners
bound to TCP ports but is being drained for maintenance.

Author: the-mikedavis

deps/rabbitmq_management/priv/www/api/index.html

@@ -1237,6 +1237,19 @@ <h2>Reference</h2>
           </p>
         </td>
       </tr>
+      <tr>
+        <td>X</td>
+        <td></td>
+        <td></td>
+        <td></td>
+        <td class="path">/api/health/checks/is-in-service</td>
+        <td>
+          Responds a 200 OK if the target node is booted, running, and ready to
+          serve clients, otherwise responds with a 503 Service Unavailable. If the
+          target node is being drained for maintenance then this check returns 503
+          Service Unavailable.
+        </td>
+      </tr>
       <tr>
         <td>X</td>
         <td></td>

deps/rabbitmq_management/src/rabbit_mgmt_dispatcher.erl

@@ -207,6 +207,7 @@ dispatcher() ->
      {"/health/checks/quorum-queues-without-elected-leaders/all-vhosts/pattern/:pattern",    rabbit_mgmt_wm_health_check_quorum_queues_without_elected_leaders_across_all_vhosts, []},
      {"/health/checks/quorum-queues-without-elected-leaders/vhost/:vhost/pattern/:pattern",  rabbit_mgmt_wm_health_check_quorum_queues_without_elected_leaders, []},
      {"/health/checks/node-is-quorum-critical",                rabbit_mgmt_wm_health_check_node_is_quorum_critical, []},
+     {"/health/checks/is-in-service",                          rabbit_mgmt_wm_health_check_is_in_service, []},
      {"/reset",                                                rabbit_mgmt_wm_reset, []},
      {"/reset/:node",                                          rabbit_mgmt_wm_reset, []},
      {"/rebalance/queues",                                     rabbit_mgmt_wm_rebalance_queues, [{queues, all}]},

deps/rabbitmq_management/src/rabbit_mgmt_wm_health_check_is_in_service.erl

@@ -0,0 +1,44 @@
+%% This Source Code Form is subject to the terms of the Mozilla Public
+%% License, v. 2.0. If a copy of the MPL was not distributed with this
+%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
+%%
+%% Copyright (c) 2025 Broadcom. All Rights Reserved. The term “Broadcom” refers to Broadcom Inc. and/or its subsidiaries. All rights reserved.
+%%
+
+-module(rabbit_mgmt_wm_health_check_is_in_service).
+
+-export([init/2]).
+-export([to_json/2, content_types_provided/2]).
+-export([variances/2]).
+
+-include("rabbit_mgmt.hrl").
+-include_lib("rabbitmq_management_agent/include/rabbit_mgmt_records.hrl").
+
+init(Req, _State) ->
+    Req1 = rabbit_mgmt_headers:set_no_cache_headers(
+             rabbit_mgmt_headers:set_common_permission_headers(
+               Req, ?MODULE), ?MODULE),
+    {cowboy_rest, Req1, #context{}}.
+
+variances(Req, Context) ->
+    {[<<"accept-encoding">>, <<"origin">>], Req, Context}.
+
+content_types_provided(ReqData, Context) ->
+   {rabbit_mgmt_util:responder_map(to_json), ReqData, Context}.
+
+to_json(ReqData, Context) ->
+    case rabbit:is_serving() of
+        true ->
+            rabbit_mgmt_util:reply(#{status => ok}, ReqData, Context);
+        false ->
+            Msg = "this rabbit node is not currently available to serve",
+            failure(Msg, ReqData, Context)
+    end.
+
+failure(Message, ReqData, Context) ->
+    Body = #{
+        status => failed,
+        reason => rabbit_data_coercion:to_binary(Message)
+    },
+    {Response, ReqData1, Context1} = rabbit_mgmt_util:reply(Body, ReqData, Context),
+    {stop, cowboy_req:reply(?HEALTH_CHECK_FAILURE_STATUS, #{}, Response, ReqData1), Context1}.

deps/rabbitmq_management/test/rabbit_mgmt_http_health_checks_SUITE.erl

@@ -50,7 +50,8 @@ all_tests() -> [
                 metadata_store_initialized_with_data_test,
                 protocol_listener_test,
                 port_listener_test,
-                certificate_expiration_test
+                certificate_expiration_test,
+                is_in_service_test
                ].
 
 %% -------------------------------------------------------------------
@@ -449,6 +450,18 @@ certificate_expiration_test(Config) ->
 
     passed.
 
+is_in_service_test(Config) ->
+    Path = "/health/checks/is-in-service",
+    Check0 = http_get(Config, Path, ?OK),
+    ?assertEqual(<<"ok">>, maps:get(status, Check0)),
+
+    true = rabbit_ct_broker_helpers:mark_as_being_drained(Config, 0),
+    Body0 = http_get_failed(Config, Path),
+    ?assertEqual(<<"failed">>, maps:get(<<"status">>, Body0)),
+    true = rabbit_ct_broker_helpers:unmark_as_being_drained(Config, 0),
+
+    passed.
+
 http_get_failed(Config, Path) ->
     {ok, {{_, Code, _}, _, ResBody}} = req(Config, get, Path, [auth_header("guest", "guest")]),
     ?assertEqual(Code, ?HEALTH_CHECK_FAILURE_STATUS),