From 299cc40ff587656140db111710bcb400825e3c3a Mon Sep 17 00:00:00 2001
From: Hampus <hampus@fluxer.app>
Date: Sun, 30 Aug 2026 23:16:53 +0200
Subject: [PATCH] fix(gateway): split inbound and outbound rpc concurrency keys
 (#2186)

---
 .../src/gateway/fluxer_gateway_config.erl      |  5 +++++
 .../src/gateway/gateway_nats_pool_conn.erl     |  4 ++--
 .../src/gateway/gateway_nats_rpc_handler.erl   |  4 ++--
 .../test/fluxer_gateway_config_tests.erl       | 18 ++++++++++++++++++
 .../src/config_loader/EnvironmentOverrides.ts  |  4 ++++
 5 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/fluxer_gateway/src/gateway/fluxer_gateway_config.erl b/fluxer_gateway/src/gateway/fluxer_gateway_config.erl
index 64c7b6682..6ca7906b4 100644
--- a/fluxer_gateway/src/gateway/fluxer_gateway_config.erl
+++ b/fluxer_gateway/src/gateway/fluxer_gateway_config.erl
@@ -99,6 +99,9 @@ env_gateway_base_config() ->
         <<"gateway_http_rpc_max_concurrency">> => env_int(
             "FLUXER_GATEWAY_HTTP_RPC_MAX_CONCURRENCY", 512
         ),
+        <<"gateway_nats_rpc_max_handlers">> => env_int(
+            "FLUXER_GATEWAY_NATS_RPC_MAX_HANDLERS", 512
+        ),
         <<"gateway_http_failure_threshold">> => env_int(
             "FLUXER_GATEWAY_HTTP_FAILURE_THRESHOLD", 6
         ),
@@ -205,6 +208,8 @@ build_core_config(Service, Internal, Nats, Proxy) ->
         nats_core_url => get_string(Nats, <<"core_url">>, "nats://127.0.0.1:4222"),
         nats_auth_token => get_string(Nats, <<"auth_token">>, ""),
         rpc_auth_token => get_string(Service, <<"rpc_auth_token">>, ""),
+        gateway_nats_rpc_max_handlers =>
+            get_int(Service, <<"gateway_nats_rpc_max_handlers">>, 512),
         identify_rate_limit_enabled => get_bool(
             Service, <<"identify_rate_limit_enabled">>, false
         )
diff --git a/fluxer_gateway/src/gateway/gateway_nats_pool_conn.erl b/fluxer_gateway/src/gateway/gateway_nats_pool_conn.erl
index fbbd53a72..0a9d67c58 100644
--- a/fluxer_gateway/src/gateway/gateway_nats_pool_conn.erl
+++ b/fluxer_gateway/src/gateway/gateway_nats_pool_conn.erl
@@ -22,7 +22,7 @@
 ]).
 
 -define(DEFAULT_POOL_SIZE, 16).
--define(DEFAULT_MAX_HANDLERS, 1024).
+-define(DEFAULT_MAX_HANDLERS, 512).
 -define(RECONNECT_BASE_DELAY_MS, 2000).
 -define(RECONNECT_MAX_DELAY_MS, 30000).
 -define(CONNECT_TIMEOUT_MS, 10000).
@@ -244,7 +244,7 @@ pool_size() ->
 
 -spec max_handlers() -> pos_integer().
 max_handlers() ->
-    case fluxer_gateway_env:get(gateway_http_rpc_max_concurrency) of
+    case fluxer_gateway_env:get(gateway_nats_rpc_max_handlers) of
         Value when is_integer(Value), Value > 0 -> Value;
         _ -> ?DEFAULT_MAX_HANDLERS
     end.
diff --git a/fluxer_gateway/src/gateway/gateway_nats_rpc_handler.erl b/fluxer_gateway/src/gateway/gateway_nats_rpc_handler.erl
index e7696d834..31911a9b3 100644
--- a/fluxer_gateway/src/gateway/gateway_nats_rpc_handler.erl
+++ b/fluxer_gateway/src/gateway/gateway_nats_rpc_handler.erl
@@ -15,7 +15,7 @@
     build_connect_opts/1
 ]).
 
--define(DEFAULT_MAX_HANDLERS, 1024).
+-define(DEFAULT_MAX_HANDLERS, 512).
 -define(RECONNECT_DELAY_MS, 2000).
 -define(CONNECT_TIMEOUT_MS, 10000).
 -define(RPC_SUBJECT_WILDCARD, <<"rpc.gateway.>">>).
@@ -218,7 +218,7 @@ schedule_reconnect(State) ->
 
 -spec max_handlers() -> pos_integer().
 max_handlers() ->
-    case fluxer_gateway_env:get(gateway_http_rpc_max_concurrency) of
+    case fluxer_gateway_env:get(gateway_nats_rpc_max_handlers) of
         Value when is_integer(Value), Value > 0 -> Value;
         _ -> ?DEFAULT_MAX_HANDLERS
     end.
diff --git a/fluxer_gateway/test/fluxer_gateway_config_tests.erl b/fluxer_gateway/test/fluxer_gateway_config_tests.erl
index 5f828a3f5..3c2fca551 100644
--- a/fluxer_gateway/test/fluxer_gateway_config_tests.erl
+++ b/fluxer_gateway/test/fluxer_gateway_config_tests.erl
@@ -127,6 +127,24 @@ env_only_push_and_http_runtime_config_test() ->
         end
     ).
 
+rpc_concurrency_keys_are_independent_test() ->
+    with_envs(
+        [
+            {"FLUXER_GATEWAY_HTTP_RPC_MAX_CONCURRENCY", "128"},
+            {"FLUXER_GATEWAY_NATS_RPC_MAX_HANDLERS", "2048"}
+        ],
+        fun() ->
+            Config = fluxer_gateway_config:load(),
+            ?assertEqual(128, maps:get(gateway_http_rpc_max_concurrency, Config)),
+            ?assertEqual(2048, maps:get(gateway_nats_rpc_max_handlers, Config))
+        end
+    ).
+
+rpc_concurrency_key_defaults_test() ->
+    Config = fluxer_gateway_config:build_config(#{}),
+    ?assertEqual(512, maps:get(gateway_nats_rpc_max_handlers, Config)),
+    ?assertEqual(512, maps:get(gateway_http_rpc_max_concurrency, Config)).
+
 optional_string_test() ->
     ?assertEqual(undefined, fluxer_gateway_config:optional_string(undefined)),
     ?assertEqual("hello", fluxer_gateway_config:optional_string(<<"hello">>)),
diff --git a/packages/config/src/config_loader/EnvironmentOverrides.ts b/packages/config/src/config_loader/EnvironmentOverrides.ts
index 8b33e579a..764b96c0e 100644
--- a/packages/config/src/config_loader/EnvironmentOverrides.ts
+++ b/packages/config/src/config_loader/EnvironmentOverrides.ts
@@ -212,6 +212,10 @@ const NAMED_FLUXER_ENV_OVERRIDES: Record<string, NamedEnvOverride> = {
 		path: ['services', 'gateway', 'gateway_http_rpc_max_concurrency'],
 		parse: parseEnvValue,
 	},
+	FLUXER_GATEWAY_NATS_RPC_MAX_HANDLERS: {
+		path: ['services', 'gateway', 'gateway_nats_rpc_max_handlers'],
+		parse: parseEnvValue,
+	},
 	FLUXER_GATEWAY_SHUTDOWN_DRAIN_WAIT_MS: {
 		path: ['services', 'gateway', 'shutdown_drain_wait_ms'],
 		parse: parseEnvValue,