Make Orchestrator metrics singleton

So that even if applications instantiate multiple Orchestrators,
"megaservice_*" metrics collect data from all of them.

Another option would be to add arguments for passing Orchestrator
instance names as metric prefixes, to name and differentiate metrics
for each Orchestrator instance.

However, that would have needed changes in 3 OPEA projects instead of
just this one, and dashboards would then need to hard-code those
per-application prefixes.

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

comps/cores/mega/orchestrator.py

@@ -29,19 +29,7 @@
 
 
 class OrchestratorMetrics:
-    # Need an static class-level ID for metric prefix because:
-    # - Prometheus requires metrics (their names) to be unique
-    _instance_id = 0
-
     def __init__(self) -> None:
-        OrchestratorMetrics._instance_id += 1
-        if OrchestratorMetrics._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()
 
@@ -50,20 +38,22 @@ def __init__(self) -> None:
         self.first_token_latency = None
         self.inter_token_latency = None
         self.request_latency = None
+        self.request_pending = None
 
         # initial methods to create the metrics
         self.token_update = self._token_update_create
         self.request_update = self._request_update_create
+        self.pending_update = self._pending_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)"
+                    "megaservice_first_token_latency", "First token latency (histogram)"
                 )
                 self.inter_token_latency = Histogram(
-                    f"{self._prefix}_inter_token_latency", "Inter-token latency (histogram)"
+                    "megaservice_inter_token_latency", "Inter-token latency (histogram)"
                 )
                 self.token_update = self._token_update_real
         return self.token_update(token_start, is_first)
@@ -73,11 +63,21 @@ def _request_update_create(self, req_start: float) -> None:
             # 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)"
+                    "megaservice_request_latency", "Whole LLM request/reply latency (histogram)"
                 )
                 self.request_update = self._request_update_real
         self.request_update(req_start)
 
+    def _pending_update_create(self, increase: bool) -> None:
+        with self._lock:
+            # in case another thread already got here
+            if self.pending_update == self._pending_update_create:
+                self.request_pending = Gauge(
+                    "megaservice_request_pending", "Count of currently pending requests (gauge)"
+                )
+                self.pending_update = self._pending_update_real
+        self.pending_update(increase)
+
     def _token_update_real(self, token_start: float, is_first: bool) -> float:
         now = time.time()
         if is_first:
@@ -89,18 +89,22 @@ def _token_update_real(self, token_start: float, is_first: bool) -> float:
     def _request_update_real(self, req_start: float) -> None:
         self.request_latency.observe(time.time() - req_start)
 
-    def pending_update(self, increase: bool) -> None:
+    def _pending_update_real(self, increase: bool) -> None:
         if increase:
             self.request_pending.inc()
         else:
             self.request_pending.dec()
 
 
+# Prometheus metrics need to be singletons, not per Orchestrator
+_metrics = OrchestratorMetrics()
+
+
 class ServiceOrchestrator(DAG):
     """Manage 1 or N micro services in a DAG through Python API."""
 
     def __init__(self) -> None:
-        self.metrics = OrchestratorMetrics()
+        self.metrics = _metrics
         self.services = {}  # all services, id -> service
         super().__init__()