[Fix] Block proxy startup when use_redis_transaction_buffer is enabled without Redis cache

When `use_redis_transaction_buffer: true` is set in general_settings but no
Redis cache is configured in litellm_settings, the proxy starts successfully
but silently drops all spend tracking data. This adds a startup validation
that raises a clear error, preventing the proxy from running in a broken state.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

litellm/proxy/proxy_server.py

@@ -871,6 +871,12 @@ async def proxy_startup_event(app: FastAPI):  # noqa: PLR0915
         redis_usage_cache=redis_usage_cache,
     )
 
+    ## Validate use_redis_transaction_buffer requires Redis cache ##
+    ProxyStartupEvent._validate_redis_transaction_buffer_config(
+        general_settings=general_settings,
+        redis_usage_cache=redis_usage_cache,
+    )
+
     ## SEMANTIC TOOL FILTER ##
     # Read litellm_settings from config for semantic filter initialization
     try:
@@ -5618,6 +5624,40 @@ class ProxyStartupEvent:
             llm_router=llm_router, redis_usage_cache=redis_usage_cache
         )
 
+    @staticmethod
+    def _validate_redis_transaction_buffer_config(
+        general_settings: dict,
+        redis_usage_cache: Optional[RedisCache],
+    ):
+        """
+        Validates that when use_redis_transaction_buffer is enabled,
+        a Redis cache is properly configured in litellm_settings.
+
+        Without Redis, spend updates are silently dropped because:
+        - In-memory queues are drained but never pushed to Redis
+        - The pod lock manager cannot acquire locks for DB commits
+        - No fallback to direct DB writes occurs
+        """
+        from litellm.proxy.db.db_transaction_queue.redis_update_buffer import (
+            RedisUpdateBuffer,
+        )
+
+        if (
+            RedisUpdateBuffer._should_commit_spend_updates_to_redis()
+            and redis_usage_cache is None
+        ):
+            raise ValueError(
+                "`use_redis_transaction_buffer` is enabled in general_settings, "
+                "but no Redis cache is configured. Spend tracking will silently "
+                "fail without Redis. Please add a Redis cache configuration in "
+                "litellm_settings:\n\n"
+                "litellm_settings:\n"
+                "  cache: true\n"
+                "  cache_params:\n"
+                "    type: redis\n"
+                "    url: os.environ/REDIS_URL\n"
+            )
+
     @classmethod
     async def _initialize_semantic_tool_filter(
         cls,

tests/test_litellm/proxy/db/db_transaction_queue/test_redis_update_buffer.py

@@ -10,6 +10,7 @@ sys.path.insert(
 )  # Adds the parent directory to the system path
 
 from litellm.proxy.db.db_transaction_queue.redis_update_buffer import RedisUpdateBuffer
+from litellm.proxy.proxy_server import ProxyStartupEvent
 from litellm.types.caching import RedisPipelineRpushOperation
 
 
@@ -192,3 +193,53 @@ async def test_get_all_transactions_from_redis_buffer_pipeline_no_redis():
     buffer = RedisUpdateBuffer(redis_cache=None)
     result = await buffer.get_all_transactions_from_redis_buffer_pipeline()
     assert result == (None, None, None, None, None, None, None)
+
+
+def test_validate_redis_transaction_buffer_raises_without_redis():
+    """
+    When use_redis_transaction_buffer=true but no Redis cache is configured,
+    the proxy should refuse to start with a clear error message.
+    """
+    general_settings = {"use_redis_transaction_buffer": True}
+
+    with patch(
+        "litellm.proxy.proxy_server.general_settings", general_settings
+    ):
+        with pytest.raises(ValueError, match="use_redis_transaction_buffer"):
+            ProxyStartupEvent._validate_redis_transaction_buffer_config(
+                general_settings=general_settings,
+                redis_usage_cache=None,
+            )
+
+
+def test_validate_redis_transaction_buffer_passes_with_redis():
+    """
+    When use_redis_transaction_buffer=true and Redis cache is configured,
+    validation should pass without error.
+    """
+    general_settings = {"use_redis_transaction_buffer": True}
+    mock_redis_cache = MagicMock()
+
+    with patch(
+        "litellm.proxy.proxy_server.general_settings", general_settings
+    ):
+        # Should not raise
+        ProxyStartupEvent._validate_redis_transaction_buffer_config(
+            general_settings=general_settings,
+            redis_usage_cache=mock_redis_cache,
+        )
+
+
+def test_validate_redis_transaction_buffer_passes_when_disabled():
+    """
+    When use_redis_transaction_buffer is not set or false,
+    validation should pass regardless of Redis configuration.
+    """
+    with patch(
+        "litellm.proxy.proxy_server.general_settings", {}
+    ):
+        # Should not raise even without Redis
+        ProxyStartupEvent._validate_redis_transaction_buffer_config(
+            general_settings={},
+            redis_usage_cache=None,
+        )