feat: Add metrics endpoint to publish socket.io metrics to prometheus

Signed-off-by: Julius Härtl <[email protected]>

.env.example

@@ -7,3 +7,7 @@ TLS=false
 TLS_KEY=
 TLS_CERT=
 JWT_SECRET_KEY=your_secret_key
+
+# Prometheus metrics endpoint
+# Set this to access the monitoring endpoint at /metrics
+# METRICS_TOKEN=

package.json

@@ -31,10 +31,12 @@
     "jsonwebtoken": "^9.0.2",
     "lodash": "^4.17.21",
     "node-fetch": "^3.3.2",
+    "prom-client": "^14.2.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "socket.io": "^4.7.5",
     "socket.io-client": "^4.7.5",
+    "socket.io-prometheus": "^0.3.0",
     "vue": "^2.7.14"
   },
   "devDependencies": {

websocket_server/app.js

@@ -4,11 +4,24 @@
  */
 
 import express from 'express'
+import { register } from 'prom-client'
+
+const METRICS_TOKEN = process.env.METRICS_TOKEN
 
 const app = express()
 
 app.get('/', (req, res) => {
 	res.send('Excalidraw collaboration server is up :)')
 })
 
+app.get('/metrics', async (req, res) => {
+	const token = req.headers.authorization?.split(' ')[1] || req.query.token
+	if (!METRICS_TOKEN || token !== METRICS_TOKEN) {
+		return res.status(403).send('Unauthorized')
+	}
+	const metrics = await register.metrics()
+	res.set('Content-Type', register.contentType)
+	res.end(metrics)
+})
+
 export default app

websocket_server/socket.js

@@ -6,6 +6,7 @@
  */
 
 import { Server as SocketIO } from 'socket.io'
+import prometheusMetrics from 'socket.io-prometheus'
 import jwt from 'jsonwebtoken'
 import { getRoomDataFromFile, roomDataStore, saveRoomDataToFile } from './roomData.js'
 import { convertArrayBufferToString, convertStringToArrayBuffer } from './utils.js'
@@ -42,6 +43,8 @@ export const initSocket = (server) => {
 
 	io.use(socketAuthenticateHandler)
 
+	prometheusMetrics(io)
+
 	io.on('connection', (socket) => {
 		setupSocketEvents(socket, io)
 	})