fix(rate_limit): flush redis cache when __init__ is triggered by changing max_active_requests (#33830)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/core/app/features/rate_limiting/rate_limit.py

@@ -19,6 +19,7 @@ class RateLimit:
     _REQUEST_MAX_ALIVE_TIME = 10 * 60  # 10 minutes
     _ACTIVE_REQUESTS_COUNT_FLUSH_INTERVAL = 5 * 60  # recalculate request_count from request_detail every 5 minutes
     _instance_dict: dict[str, "RateLimit"] = {}
+    max_active_requests: int
 
     def __new__(cls, client_id: str, max_active_requests: int):
         if client_id not in cls._instance_dict:
@@ -27,7 +28,13 @@ class RateLimit:
         return cls._instance_dict[client_id]
 
     def __init__(self, client_id: str, max_active_requests: int):
+        flush_cache = hasattr(self, "max_active_requests") and self.max_active_requests != max_active_requests
         self.max_active_requests = max_active_requests
+        # Only flush here if this instance has already been fully initialized,
+        # i.e. the Redis key attributes exist. Otherwise, rely on the flush at
+        # the end of initialization below.
+        if flush_cache and hasattr(self, "active_requests_key") and hasattr(self, "max_active_requests_key"):
+            self.flush_cache(use_local_value=True)
         # must be called after max_active_requests is set
         if self.disabled():
             return
@@ -41,8 +48,6 @@ class RateLimit:
         self.flush_cache(use_local_value=True)
 
     def flush_cache(self, use_local_value=False):
-        if self.disabled():
-            return
         self.last_recalculate_time = time.time()
         # flush max active requests
         if use_local_value or not redis_client.exists(self.max_active_requests_key):
@@ -50,7 +55,8 @@ class RateLimit:
         else:
             self.max_active_requests = int(redis_client.get(self.max_active_requests_key).decode("utf-8"))
             redis_client.expire(self.max_active_requests_key, timedelta(days=1))
-
+        if self.disabled():
+            return
         # flush max active requests (in-transit request list)
         if not redis_client.exists(self.active_requests_key):
             return

api/tests/unit_tests/core/app/features/rate_limiting/test_rate_limit.py

@@ -68,8 +68,8 @@ class TestRateLimit:
         assert rate_limit.disabled()
         assert not hasattr(rate_limit, "initialized")
 
-    def test_should_skip_reinitialization_of_existing_instance(self, redis_patch):
-        """Test that existing instance doesn't reinitialize."""
+    def test_should_flush_cache_when_reinitializing_existing_instance(self, redis_patch):
+        """Test existing instance refreshes Redis cache on reinitialization."""
         redis_patch.configure_mock(
             **{
                 "exists.return_value": False,
@@ -82,7 +82,37 @@ class TestRateLimit:
 
         RateLimit("client1", 10)
 
+        redis_patch.setex.assert_called_once_with(
+            "dify:rate_limit:client1:max_active_requests",
+            timedelta(days=1),
+            10,
+        )
+
+    def test_should_reinitialize_after_being_disabled(self, redis_patch):
+        """Test disabled instance can be reinitialized and writes max_active_requests to Redis."""
+        redis_patch.configure_mock(
+            **{
+                "exists.return_value": False,
+                "setex.return_value": True,
+            }
+        )
+
+        # First construct with max_active_requests = 0 (disabled), which should skip initialization.
+        RateLimit("client1", 0)
+
+        # Redis should not have been written to during disabled initialization.
         redis_patch.setex.assert_not_called()
+        redis_patch.reset_mock()
+
+        # Reinitialize with a positive max_active_requests value; this should not raise
+        # and must write the max_active_requests key to Redis.
+        RateLimit("client1", 10)
+
+        redis_patch.setex.assert_called_once_with(
+            "dify:rate_limit:client1:max_active_requests",
+            timedelta(days=1),
+            10,
+        )
 
     def test_should_be_disabled_when_max_requests_is_zero_or_negative(self):
         """Test disabled state for zero or negative limits."""