Redis: Validate min version before instrumenting (#174)

* Validate min redis version before instrumenting

* Make sure not to send empty trace payloads

* Code comment

Author: pglombardo

instana/agent.py

@@ -214,6 +214,11 @@ def report_traces(self, spans):
         Used to report entity data (metrics & snapshot) to the host agent.
         """
         try:
+            # Concurrency double check:  Don't report if we don't have
+            # any spans
+            if len(spans) == 0:
+                return 0
+
             response = None
             response = self.client.post(self.__traces_url(),
                                         data=self.to_json(spans),

instana/instrumentation/redis.py

@@ -8,7 +8,7 @@
 try:
     import redis
 
-    if redis.VERSION < (3, 0, 0):
+    if ((redis.VERSION >= (2, 10, 6)) and (redis.VERSION < (3, 0, 0))):
 
         @wrapt.patch_function_wrapper('redis.client','StrictRedis.execute_command')
         def execute_command_with_instana(wrapped, instance, args, kwargs):
@@ -76,6 +76,7 @@ def execute_with_instana(wrapped, instance, args, kwargs):
 
         logger.debug("Instrumenting redis")
     else:
-        logger.debug("redis >=3.0.0 not supported (yet)")
+        logger.debug("redis <= 2.10.5 >=3.0.0 not supported.")
+        logger.debug("  --> https://docs.instana.io/ecosystem/python/supported-versions/#tracing")
 except ImportError:
     pass