make metrics from carbon-cache go via relay config

lib/carbon/instrumentation.py

@@ -170,7 +170,7 @@ def cache_record(metric, value):
     else:
       fullMetric = '%s.agents.%s-%s.%s' % (prefix, HOSTNAME, settings.instance, metric)
     datapoint = (time.time(), value)
-    cache.MetricCache().store(fullMetric, datapoint)
+    state.client_manager.sendDatapoint(fullMetric, datapoint)
 
 
 def relay_record(metric, value):

lib/carbon/routers.py

@@ -31,6 +31,29 @@ def getDestinations(self, key):
     raise NotImplementedError()
 
 
+class ConstantRouter(DatapointRouter):
+  plugin_name = 'constant'
+
+  def __init__(self, settings):
+    self.destinations = set()
+
+  def addDestination(self, destination):
+    self.destinations.add(destination)
+
+  def removeDestination(self, destination):
+    self.destinations.discard(destination)
+
+  def hasDestination(self, destination):
+    return destination in self.destinations
+
+  def countDestinations(self):
+    return len(self.destinations)
+
+  def getDestinations(self, key):
+    for destination in self.destinations:
+      yield destination
+
+
 class RelayRulesRouter(DatapointRouter):
   plugin_name = 'rules'
 

lib/carbon/service.py

@@ -87,6 +87,7 @@ def setupPipeline(pipeline, root_service, settings):
       setupRelayProcessor(root_service, settings)
     elif processor == 'write':
       setupWriterProcessor(root_service, settings)
+      setupRelayProcessor(root_service, settings)
     else:
       raise ValueError("Invalid pipeline processor '%s'" % processor)