ref(cbrs): no more default routing decision (#7421)

Not sure what the vision was with having a default routing decision that
gets passed into `get_routing_decision()` which gives you a new routing
decision (and this fails open too so if things go wrong you get a
sensible default routing decision anyways). Just keep track of routing
context instead

---------

Co-authored-by: Rachel Chen <[email protected]>

Author: xurui-c

snuba/web/rpc/__init__.py

@@ -31,7 +31,6 @@
     RPCRequestException,
     convert_rpc_exception_to_proto,
 )
-from snuba.web.rpc.storage_routing.defaults import get_default_routing_decision
 from snuba.web.rpc.storage_routing.load_retriever import get_cluster_loadinfo
 from snuba.web.rpc.storage_routing.routing_strategies.storage_routing import (
     RoutingContext,
@@ -135,7 +134,6 @@ class RPCEndpoint(Generic[Tin, Tout], metaclass=RegisteredClass):
     def __init__(self, metrics_backend: MetricsBackend | None = None) -> None:
         self._timer = Timer("endpoint_timing")
         self._metrics_backend = metrics_backend or environment.metrics
-        self.routing_decision = get_default_routing_decision(None)
 
     @classmethod
     def request_class(cls) -> Type[Tin]:
@@ -193,7 +191,7 @@ def execute(self, in_msg: Tin) -> Tout:
         span = scope.span
         if span is not None:
             span.description = self.config_key()
-        self.routing_decision.routing_context = RoutingContext(timer=self._timer, in_msg=in_msg)
+        self.routing_context = RoutingContext(timer=self._timer, in_msg=in_msg)
 
         self.__before_execute(in_msg)
         error: Exception | None = None
@@ -265,13 +263,8 @@ def __before_execute(self, in_msg: Tin) -> None:
         if state.get_config("storage_routing.enable_get_cluster_loadinfo", True):
             get_cluster_loadinfo()
 
-        selected_strategy = RoutingStrategySelector().select_routing_strategy(
-            self.routing_decision.routing_context
-        )
-        self.routing_decision.strategy = selected_strategy
-        self.routing_decision = selected_strategy.get_routing_decision(
-            self.routing_decision.routing_context
-        )
+        selected_strategy = RoutingStrategySelector().select_routing_strategy(self.routing_context)
+        self.routing_decision = selected_strategy.get_routing_decision(self.routing_context)
         self._timer.mark("rpc_start")
         self._before_execute(in_msg)