Fix: remove the check for the Server header of the Instana agent.

The check for the Server header of the Instana agent can break the announce
procedure in service meshes when there is a proxy between the tracer and the
Instana agent. This happens because some proxies do not forward the original
Server header. So instead, the collector checks whether the HTTP status code
is in the 2xx range.

Signed-off-by: Paulo Vital <[email protected]>

Author: pvital

instana/agent/host.py

@@ -41,7 +41,6 @@ class HostAgent(BaseAgent):
     """
     AGENT_DISCOVERY_PATH = "com.instana.plugin.python.discovery"
     AGENT_DATA_PATH = "com.instana.plugin.python.%d"
-    AGENT_HEADER = "Instana Agent"
 
     def __init__(self):
         super(HostAgent, self).__init__()
@@ -157,15 +156,16 @@ def is_agent_listening(self, host, port):
         result = False
         try:
             url = "http://%s:%s/" % (host, port)
-            response = self.client.get(url, timeout=0.8)
+            response = self.client.get(url, timeout=5)
 
-            server_header = response.headers["Server"]
-            if server_header == self.AGENT_HEADER:
+            if 200 <= response.status_code < 300:
                 logger.debug("Instana host agent found on %s:%d", host, port)
                 result = True
             else:
-                logger.debug("...something is listening on %s:%d but it's not the Instana Host Agent: %s",
-                             host, port, server_header)
+                logger.debug("The attempt to connect to the Instana host "\
+                             "agent on %s:%d has failed with an unexpected " \
+                             "status code. Expected HTTP 200 but received: %d",
+                             host, port, response.status_code)
         except Exception:
             logger.debug("Instana Host Agent not found on %s:%d", host, port)
         return result

tests/platforms/test_host.py

@@ -236,3 +236,41 @@ def test_announce_fails_with_missing_uuid(self, mock_requests_session_put):
         self.assertEqual(len(log.output), 1)
         self.assertEqual(len(log.records), 1)
         self.assertIn('response payload has no agentUuid', log.output[0])
+
+
+    @patch.object(requests.Session, "get")
+    def test_agent_connection_attempt(self, mock_requests_session_get):
+        mock_response = MagicMock()
+        mock_response.status_code = 200
+        mock_requests_session_get.return_value = mock_response
+
+        self.create_agent_and_setup_tracer()
+        host = self.agent.options.agent_host
+        port = self.agent.options.agent_port
+        msg = f"Instana host agent found on {host}:{port}"
+        
+        with self.assertLogs(logger, level='DEBUG') as log:
+            result = self.agent.is_agent_listening(host, port)
+
+        self.assertTrue(result)
+        self.assertIn(msg, log.output[0])
+
+
+    @patch.object(requests.Session, "get")
+    def test_agent_connection_attempt_fails_with_404(self, mock_requests_session_get):
+        mock_response = MagicMock()
+        mock_response.status_code = 404
+        mock_requests_session_get.return_value = mock_response
+
+        self.create_agent_and_setup_tracer()
+        host = self.agent.options.agent_host
+        port = self.agent.options.agent_port
+        msg = "The attempt to connect to the Instana host agent on " \
+              f"{host}:{port} has failed with an unexpected status code. " \
+              f"Expected HTTP 200 but received: {mock_response.status_code}"
+
+        with self.assertLogs(logger, level='DEBUG') as log:
+            result = self.agent.is_agent_listening(host, port)
+
+        self.assertFalse(result)
+        self.assertIn(msg, log.output[0])