Add new local random exchange type.

This exchange type will only bind classic queues and will only return
routes for queues that are local to the publishing connection. If more than
one queue is bound it will make a random choice of the locally bound queues.

This exchange type is suitable as a component in systems that run
highly available low-latency RPC workloads.

Co-authored-by: Marcial Rosales <mrosales@pivotal.io>

Author: kjnilsson

deps/rabbit/BUILD.bazel

@@ -1062,6 +1062,14 @@ rabbitmq_integration_suite(
     ],
 )
 
+rabbitmq_integration_suite(
+    name = "rabbit_local_random_exchange_SUITE",
+    size = "small",
+    additional_beam = [
+        ":test_queue_utils_beam",
+    ],
+)
+
 rabbitmq_integration_suite(
     name = "rabbit_direct_reply_to_prop_SUITE",
     size = "medium",

deps/rabbit/app.bzl

@@ -131,6 +131,7 @@ def all_beam_files(name = "all_beam_files"):
             "src/rabbit_exchange_type_fanout.erl",
             "src/rabbit_exchange_type_headers.erl",
             "src/rabbit_exchange_type_invalid.erl",
+            "src/rabbit_exchange_type_local_random.erl",
             "src/rabbit_exchange_type_topic.erl",
             "src/rabbit_feature_flags.erl",
             "src/rabbit_ff_controller.erl",
@@ -391,6 +392,7 @@ def all_test_beam_files(name = "all_test_beam_files"):
             "src/rabbit_exchange_type_fanout.erl",
             "src/rabbit_exchange_type_headers.erl",
             "src/rabbit_exchange_type_invalid.erl",
+            "src/rabbit_exchange_type_local_random.erl",
             "src/rabbit_exchange_type_topic.erl",
             "src/rabbit_feature_flags.erl",
             "src/rabbit_ff_controller.erl",
@@ -670,6 +672,7 @@ def all_srcs(name = "all_srcs"):
             "src/rabbit_exchange_type_fanout.erl",
             "src/rabbit_exchange_type_headers.erl",
             "src/rabbit_exchange_type_invalid.erl",
+            "src/rabbit_exchange_type_local_random.erl",
             "src/rabbit_exchange_type_topic.erl",
             "src/rabbit_feature_flags.erl",
             "src/rabbit_ff_controller.erl",
@@ -2048,7 +2051,6 @@ def test_suite_beam_files(name = "test_suite_beam_files"):
         erlc_opts = "//:test_erlc_opts",
         deps = ["//deps/amqp_client:erlang_app"],
     )
-
     erlang_bytecode(
         name = "test_event_recorder_beam",
         testonly = True,
@@ -2129,3 +2131,12 @@ def test_suite_beam_files(name = "test_suite_beam_files"):
         erlc_opts = "//:test_erlc_opts",
         deps = ["//deps/amqp_client:erlang_app"],
     )
+    erlang_bytecode(
+        name = "rabbit_local_random_exchange_SUITE_beam_files",
+        testonly = True,
+        srcs = ["test/rabbit_local_random_exchange_SUITE.erl"],
+        outs = ["test/rabbit_local_random_exchange_SUITE.beam"],
+        app_name = "rabbit",
+        erlc_opts = "//:test_erlc_opts",
+        deps = ["//deps/amqp_client:erlang_app"],
+    )

deps/rabbit/src/rabbit_exchange_type_local_random.erl

@@ -0,0 +1,116 @@
+%% 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) 2007-2023 VMware, Inc. or its affiliates.  All rights reserved.
+%%
+
+-module(rabbit_exchange_type_local_random).
+-behaviour(rabbit_exchange_type).
+-include_lib("rabbit_common/include/rabbit.hrl").
+
+-rabbit_feature_flag({?MODULE,
+                      #{desc => "Local random exchange",
+                        stability => stable
+                       }}).
+
+-rabbit_boot_step({?MODULE,
+                   [{description, "exchange type local random"},
+                    {mfa, {rabbit_registry, register,
+                           [exchange, <<"x-local-random">>, ?MODULE]}},
+                    {requires, rabbit_registry},
+                    {enables, kernel_ready}
+                   ]}).
+
+-export([add_binding/3,
+         assert_args_equivalence/2,
+         create/2,
+         delete/2,
+         policy_changed/2,
+         description/0,
+         recover/2,
+         remove_bindings/3,
+         validate_binding/2,
+         route/3,
+         serialise_events/0,
+         validate/1,
+         info/1,
+         info/2
+        ]).
+
+description() ->
+    [{name, <<"x-local-random">>},
+     {description, <<"Picks one random local binding (queue) to route via (to).">>}].
+
+route(#exchange{name = Name}, _Msg, _Opts) ->
+    Matches = rabbit_router:match_routing_key(Name, [<<>>]),
+    case lists:filter(fun filter_local_queue/1, Matches) of
+        [] ->
+            [];
+        [_] = One ->
+            One;
+        LocalMatches ->
+            Rand = rand:uniform(length(LocalMatches)),
+            [lists:nth(Rand, LocalMatches)]
+    end.
+
+info(_X) -> [].
+info(_X, _) -> [].
+serialise_events() -> false.
+validate(_X) ->
+    case rabbit_feature_flags:is_enabled(?MODULE) of
+        true ->
+            ok;
+        false ->
+            rabbit_misc:amqp_error(
+              precondition_failed,
+              "x-local-random exchange feature not available", [],
+              'exchange.declare')
+    end.
+
+create(_Serial, _X) -> ok.
+recover(_X, _Bs) -> ok.
+delete(_Serial, _X) -> ok.
+policy_changed(_X1, _X2) -> ok.
+add_binding(_Serial, _X, _B) -> ok.
+remove_bindings(_Serial, _X, _Bs) -> ok.
+
+validate_binding(_X, #binding{destination = Dest,
+                              key = <<>>}) ->
+    case rabbit_amqqueue:lookup(Dest) of
+        {ok, Q} ->
+            case amqqueue:get_type(Q) of
+                rabbit_classic_queue ->
+                    ok;
+                Type ->
+                    {error, {binding_invalid,
+                             "Queue type ~ts not valid for this exchange type",
+                             [Type]}}
+            end;
+        _ ->
+            {error, {binding_invalid,
+                     "Destination not found",
+                     []}}
+    end;
+validate_binding(_X, #binding{key = BKey}) ->
+    {error, {binding_invalid,
+             "Non empty binding '~s' key not permitted",
+             [BKey]}}.
+
+assert_args_equivalence(X, Args) ->
+    rabbit_exchange:assert_args_equivalence(X, Args).
+
+filter_local_queue(QName) ->
+    %% TODO: introduce lookup function that _only_ gets the pid
+    case rabbit_amqqueue:lookup(QName) of
+        {ok, Q} ->
+            case amqqueue:get_pid(Q) of
+                Pid when is_pid(Pid) andalso
+                         node(Pid) =:= node() ->
+                    is_process_alive(Pid);
+                _ ->
+                    false
+            end;
+        _ ->
+            false
+    end.

deps/rabbit/test/quorum_queue_SUITE.erl

@@ -225,7 +225,8 @@ init_per_group(Group, Config) ->
             Config1 = rabbit_ct_helpers:set_config(Config,
                                                    [{rmq_nodes_count, ClusterSize},
                                                     {rmq_nodename_suffix, Group},
-                                                    {tcp_ports_base}]),
+                                                    {tcp_ports_base, {skip_n_nodes, ClusterSize}}
+                                                   ]),
             Config1b = rabbit_ct_helpers:set_config(Config1, [{net_ticktime, 10}]),
             Ret = rabbit_ct_helpers:run_steps(Config1b,
                                               [fun merge_app_env/1 ] ++
@@ -263,7 +264,7 @@ init_per_testcase(Testcase, Config) when Testcase == reconnect_consumer_and_publ
     Config2 = rabbit_ct_helpers:set_config(Config1,
                                            [{rmq_nodes_count, 3},
                                             {rmq_nodename_suffix, Testcase},
-                                            {tcp_ports_base},
+                                            {tcp_ports_base, {skip_n_nodes, 3}},
                                             {queue_name, Q},
                                             {alt_queue_name, <<Q/binary, "_alt">>}
                                            ]),