fix(router.py): add validation for how router fallbacks are setup

prevent user errors

litellm/proxy/_super_secret_config.yaml

@@ -18,8 +18,6 @@ model_list:
     model: azure/chatgpt-v-2
     api_key: os.environ/AZURE_API_KEY
     api_base: os.environ/AZURE_API_BASE
-    input_cost_per_token: 0.0
-    output_cost_per_token: 0.0
 - model_name: bert-classifier
   litellm_params:
     model: huggingface/text-classification/shahrukhx01/question-vs-statement-classifier
@@ -31,8 +29,7 @@ router_settings:
   enable_pre_call_checks: true
 
 litellm_settings:
-  set_verbose: True
-  fallbacks: [{"gpt-3.5-turbo-012": ["gpt-3.5-turbo-0125-preview"]}]
+  fallbacks: [{"gpt-3.5-turbo-012": ["azure-gpt-3.5-turbo"]}]
   # service_callback: ["prometheus_system"]
   # success_callback: ["prometheus"]
   # failure_callback: ["prometheus"]

litellm/router.py

@@ -262,13 +262,23 @@ class Router:
 
         self.retry_after = retry_after
         self.routing_strategy = routing_strategy
-        self.fallbacks = fallbacks or litellm.fallbacks
+
+        ## SETTING FALLBACKS ##
+        ### validate if it's set + in correct format
+        _fallbacks = fallbacks or litellm.fallbacks
+
+        self.validate_fallbacks(fallback_param=_fallbacks)
+        ### set fallbacks
+        self.fallbacks = _fallbacks
+
         if default_fallbacks is not None or litellm.default_fallbacks is not None:
             _fallbacks = default_fallbacks or litellm.default_fallbacks
+            self.validate_fallbacks(fallback_param=_fallbacks)
             if self.fallbacks is not None:
                 self.fallbacks.append({"*": _fallbacks})
             else:
                 self.fallbacks = [{"*": _fallbacks}]
+
         self.context_window_fallbacks = (
             context_window_fallbacks or litellm.context_window_fallbacks
         )
@@ -336,6 +346,21 @@ class Router:
         if self.alerting_config is not None:
             self._initialize_alerting()
 
+    def validate_fallbacks(self, fallback_param: Optional[List]):
+        if fallback_param is None:
+            return
+        if len(fallback_param) > 0:  # if set
+            ## for dictionary in list, check if only 1 key in dict
+            for _dict in fallback_param:
+                assert isinstance(_dict, dict), "Item={}, not a dictionary".format(
+                    _dict
+                )
+                assert (
+                    len(_dict.keys()) == 1
+                ), "Only 1 key allows in dictionary. You set={} for dict={}".format(
+                    len(_dict.keys()), _dict
+                )
+
     def routing_strategy_init(self, routing_strategy: str, routing_strategy_args: dict):
         if routing_strategy == "least-busy":
             self.leastbusy_logger = LeastBusyLoggingHandler(