Create token metrics only when they are available (opea-project#1092)

* Create token metrics only when they are available

This avoids generation of useless token/request histogram metrics
for services that use Orchestrator class, but never call its token
processing functionality.

(Helps in differentiating frontend megaservice metrics from backend
megaservice ones, especially when multiple OPEA applications run in
the same cluster.)

Also change Orchestrator CI test workaround to use unique prefix for
each metric instance, instead of metrics being (singleton) class
variables.

Signed-off-by: Eero Tamminen <[email protected]>

* Add locking for latency metric creation / method change

As that that could be called from multiple request handling threads.

Signed-off-by: Eero Tamminen <[email protected]>

---------

Signed-off-by: Eero Tamminen <[email protected]>
Co-authored-by: Malini Bhandaru <[email protected]>

comps/cores/mega/orchestrator.py

@@ -7,6 +7,7 @@
 import json
 import os
 import re
+import threading
 import time
 from typing import Dict, List
 
@@ -27,28 +28,66 @@
 
 
 class OrchestratorMetrics:
-    # Because:
+    # Need an instance ID for metric prefix because:
+    # - Orchestror instances are not named
     # - CI creates several orchestrator instances
-    # - Prometheus requires metrics to be singletons
-    # - Oorchestror instances are not provided their own names
-    # Metrics are class members with "megaservice" name prefix
-    first_token_latency = Histogram("megaservice_first_token_latency", "First token latency (histogram)")
-    inter_token_latency = Histogram("megaservice_inter_token_latency", "Inter-token latency (histogram)")
-    request_latency = Histogram("megaservice_request_latency", "Whole request/reply latency (histogram)")
-    request_pending = Gauge("megaservice_request_pending", "Count of currently pending requests (gauge)")
+    # - Prometheus requires metrics (their names) to be unique
+    _instance_id = 0
 
     def __init__(self) -> None:
-        pass
+        self._instance_id += 1
+        if self._instance_id > 1:
+            self._prefix = f"megaservice{self._instance_id}"
+        else:
+            self._prefix = "megaservice"
+
+        self.request_pending = Gauge(f"{self._prefix}_request_pending", "Count of currently pending requests (gauge)")
+
+        # locking for latency metric creation / method change
+        self._lock = threading.Lock()
+
+        # Metrics related to token processing are created on demand,
+        # to avoid bogus ones for services that never handle tokens
+        self.first_token_latency = None
+        self.inter_token_latency = None
+        self.request_latency = None
+
+        # initial methods to create the metrics
+        self.token_update = self._token_update_create
+        self.request_update = self._request_update_create
+
+    def _token_update_create(self, token_start: float, is_first: bool) -> float:
+        with self._lock:
+            # in case another thread already got here
+            if self.token_update == self._token_update_create:
+                self.first_token_latency = Histogram(
+                    f"{self._prefix}_first_token_latency", "First token latency (histogram)"
+                )
+                self.inter_token_latency = Histogram(
+                    f"{self._prefix}_inter_token_latency", "Inter-token latency (histogram)"
+                )
+                self.token_update = self._token_update_real
+        return self.token_update(token_start, is_first)
+
+    def _request_update_create(self, req_start: float) -> None:
+        with self._lock:
+            # in case another thread already got here
+            if self.request_update == self._request_update_create:
+                self.request_latency = Histogram(
+                    f"{self._prefix}_request_latency", "Whole LLM request/reply latency (histogram)"
+                )
+                self.request_update = self._request_update_real
+        self.request_update(req_start)
 
-    def token_update(self, token_start: float, is_first: bool) -> float:
+    def _token_update_real(self, token_start: float, is_first: bool) -> float:
         now = time.time()
         if is_first:
             self.first_token_latency.observe(now - token_start)
         else:
             self.inter_token_latency.observe(now - token_start)
         return now
 
-    def request_update(self, req_start: float) -> None:
+    def _request_update_real(self, req_start: float) -> None:
         self.request_latency.observe(time.time() - req_start)
 
     def pending_update(self, increase: bool) -> None: