From 3311e9d354582e88333cddc5504e7c019c550d0f Mon Sep 17 00:00:00 2001
From: Nawaz Dhandala <hello@nawazdhandala.com>
Date: Sun, 28 Dec 2025 13:33:52 +0000
Subject: [PATCH] refactor: update metrics endpoint to return pending monitor
 count for KEDA autoscaling

---
 Probe/API/Metrics.ts       | 31 ++++++++++++--------
 ProbeIngest/API/Monitor.ts | 58 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 12 deletions(-)

diff --git a/Probe/API/Metrics.ts b/Probe/API/Metrics.ts
index 9864276077..ab39c56060 100644
--- a/Probe/API/Metrics.ts
+++ b/Probe/API/Metrics.ts
@@ -19,6 +19,7 @@ import ProxyConfig from "../Utils/ProxyConfig";
 const router: ExpressRouter = Express.getRouter();
 
 // Metrics endpoint for Keda autoscaling
+// Returns the number of monitors pending to be probed by this probe
 router.get(
   "/queue-size",
   async (
@@ -28,11 +29,14 @@ router.get(
   ): Promise<void> => {
     try {
       // Get the pending monitor count for this specific probe from ProbeIngest API
-      const queueSizeUrl: URL = URL.fromString(
+      // This is the correct metric - the number of monitors waiting to be probed
+      const pendingMonitorsUrl: URL = URL.fromString(
         PROBE_INGEST_URL.toString(),
-      ).addRoute("/metrics/queue-size");
+      ).addRoute("/monitor/pending-count");
 
-      logger.debug("Fetching queue size from ProbeIngest API");
+      logger.debug(
+        "Fetching pending monitor count from ProbeIngest API for KEDA scaling",
+      );
 
       // Use probe authentication (probe key and probe ID)
       const requestBody: JSONObject = ProbeAPIRequest.getDefaultRequestBody();
@@ -40,37 +44,40 @@ router.get(
       const result: HTTPResponse<JSONObject> | HTTPErrorResponse =
         await API.fetch<JSONObject>({
           method: HTTPMethod.POST,
-          url: queueSizeUrl,
+          url: pendingMonitorsUrl,
           data: requestBody,
           headers: {},
-          options: { ...ProxyConfig.getRequestProxyAgents(queueSizeUrl) },
+          options: { ...ProxyConfig.getRequestProxyAgents(pendingMonitorsUrl) },
         });
 
       if (result instanceof HTTPErrorResponse) {
-        logger.error("Error fetching queue size from ProbeIngest API");
+        logger.error("Error fetching pending monitor count from ProbeIngest API");
         logger.error(result);
         throw result;
       }
 
-      logger.debug("Queue size fetched successfully from ProbeIngest API");
+      logger.debug(
+        "Pending monitor count fetched successfully from ProbeIngest API",
+      );
       logger.debug(result.data);
 
-      // Extract queueSize from the response
-      let queueSize: number = (result.data["queueSize"] as number) || 0;
+      // Extract count from the response - this is the number of monitors pending to be probed
+      let queueSize: number = (result.data["count"] as number) || 0;
 
       // if string then convert to number
-
       if (typeof queueSize === "string") {
         const parsedQueueSize: number = parseInt(queueSize, 10);
         if (!isNaN(parsedQueueSize)) {
           queueSize = parsedQueueSize;
         } else {
-          logger.warn("Queue size is not a valid number, defaulting to 0");
+          logger.warn(
+            "Pending monitor count is not a valid number, defaulting to 0",
+          );
           queueSize = 0;
         }
       }
 
-      logger.debug(`Queue size fetched: ${queueSize}`);
+      logger.debug(`Pending monitor count for KEDA: ${queueSize}`);
 
       return Response.sendJsonObjectResponse(req, res, {
         queueSize: queueSize,
diff --git a/ProbeIngest/API/Monitor.ts b/ProbeIngest/API/Monitor.ts
index 85279de752..84619d626a 100644
--- a/ProbeIngest/API/Monitor.ts
+++ b/ProbeIngest/API/Monitor.ts
@@ -277,6 +277,64 @@ router.get(
   },
 );
 
+// This API returns the count of monitors pending to be probed for the authenticated probe.
+// Used by KEDA for autoscaling probes based on pending monitor count.
+router.post(
+  "/monitor/pending-count",
+  ProbeAuthorization.isAuthorizedServiceMiddleware,
+  async (
+    req: ExpressRequest,
+    res: ExpressResponse,
+    next: NextFunction,
+  ): Promise<void> => {
+    try {
+      if (
+        !(req as ProbeExpressRequest).probe ||
+        !(req as ProbeExpressRequest).probe?.id
+      ) {
+        logger.error("Probe not found for pending-count request");
+
+        return Response.sendErrorResponse(
+          req,
+          res,
+          new BadDataException("Probe not found"),
+        );
+      }
+
+      const probeId: ObjectID = (req as ProbeExpressRequest).probe!.id!;
+
+      if (!probeId) {
+        logger.error("Probe ID not found for pending-count request");
+
+        return Response.sendErrorResponse(
+          req,
+          res,
+          new BadDataException("Probe not found"),
+        );
+      }
+
+      // Get count of monitors pending to be probed
+      const monitorProbesCount: PositiveNumber =
+        await MonitorProbeService.countBy({
+          query: getMonitorFetchQuery(probeId),
+          props: {
+            isRoot: true,
+          },
+        });
+
+      logger.debug(
+        `Pending monitor count for probe ${probeId.toString()}: ${monitorProbesCount.toNumber()}`,
+      );
+
+      return Response.sendJsonObjectResponse(req, res, {
+        count: monitorProbesCount.toNumber(),
+      });
+    } catch (err) {
+      return next(err);
+    }
+  },
+);
+
 router.post(
   "/monitor/list",
   ProbeAuthorization.isAuthorizedServiceMiddleware,