docker healthcheck api thingy

server/src/services/healthService/index.js

@@ -2,8 +2,9 @@
 // Purpose: Defines the health Service module and the helpers/state used by this service unit.
 // Scope: Keeps runtime behavior unchanged while isolating responsibilities into a clear module boundary.
 const fsp = require('fs/promises');
+const fs = require('fs');
 const path = require('path');
-const { resolveRoverSnapshotDir } = require('../../helpers/dataPaths');
+const { resolveDataDir, resolveRoverSnapshotDir } = require('../../helpers/dataPaths');
 const roverManager = require('../roverManager');
 const { getRoomCameras } = require('../roomCameraService');
 const { getRoomCameraState } = require('../roomCameraService');
@@ -13,6 +14,8 @@ const ROVER_SNAPSHOT_DIR = resolveRoverSnapshotDir();
 const HEALTH_INTERVAL_MS = 5000;
 const ROOM_CAMERA_STALE_MS = 5000;
 const ROVER_SNAPSHOT_STALE_MS = 5000;
+const MEDIAMTX_HEALTH_URL = 'http://127.0.0.1:9998/metrics';
+const MEDIAMTX_HEALTH_TIMEOUT_MS = 1500;
 
 let latest = {
   updatedAt: Date.now(),
@@ -88,6 +91,49 @@ function getHealthSnapshot() {
   return latest;
 }
 
+async function getContainerHealth() {
+  let dataDirectory = false;
+  let mediaMtx = false;
+
+  try {
+    /*
+      The mounted data root is the container's only persistent storage. Check
+      the directory itself instead of creating a probe file on every request;
+      this proves that the running application user can reach the mount without
+      adding health-check writes to backups or administrative file listings.
+    */
+    await fsp.access(resolveDataDir(), fs.constants.R_OK | fs.constants.W_OK);
+    dataDirectory = true;
+  } catch {
+    dataDirectory = false;
+  }
+
+  try {
+    /*
+      MediaMTX already exposes metrics only on loopback, so it is also the
+      smallest reliable readiness probe. Reading the response closes the body
+      before this request completes and avoids accumulating idle connections
+      across Docker's recurring health checks.
+    */
+    const response = await fetch(MEDIAMTX_HEALTH_URL, {
+      signal: AbortSignal.timeout(MEDIAMTX_HEALTH_TIMEOUT_MS),
+    });
+    await response.text();
+    mediaMtx = response.ok;
+  } catch {
+    mediaMtx = false;
+  }
+
+  return {
+    healthy: dataDirectory && mediaMtx,
+    checks: {
+      dataDirectory,
+      mediaMtx,
+    },
+  };
+}
+
 module.exports = {
+  getContainerHealth,
   getHealthSnapshot,
 };