Upgrade prom-client and yargs

lib/metrics.js

@@ -9,14 +9,14 @@ exports.startMonitoring = (enable, eventBus) => {
 
     const client = require('prom-client');
 
-    const requestDuration = new client.Summary(
-        'http_request_duration_milliseconds',
-        'App response time',
-        ['path', 'method', 'status'],
-        {
-            percentiles: [0.1, 0.5, 0.9, 0.99],
-        }
-    );
+    client.collectDefaultMetrics();
+
+    const requestDuration = new client.Summary({
+        name: 'http_request_duration_milliseconds',
+        help: 'App response time',
+        labelNames: ['path', 'method', 'status'],
+        percentiles: [0.1, 0.5, 0.9, 0.99],
+    });
 
     eventBus.on(events.REQUEST_TIME, ({ path, method, time, statusCode }) => {
         requestDuration.labels(path, method, statusCode).observe(time);

lib/metrics.test.js

@@ -5,7 +5,7 @@ const { EventEmitter } = require('events');
 const eventBus = new EventEmitter();
 const { REQUEST_TIME } = require('./events');
 const { startMonitoring } = require('./metrics');
-const prometheusRegister = require('prom-client/lib/register');
+const { register: prometheusRegister } = require('prom-client');
 
 test('should collect metrics for requests', t => {
     startMonitoring(true, eventBus);

lib/routes/backstage.js

@@ -1,14 +1,14 @@
 'use strict';
 
 const { Router } = require('express');
-const prometheusRegister = require('prom-client/lib/register');
+const { register: prometheusRegister } = require('prom-client');
 
 exports.router = config => {
     const router = Router();
 
     if (config.serverMetrics) {
         router.get('/prometheus', (req, res) => {
-            res.writeHead(200, { 'Content-Type': 'text/plain' });
+            res.set('Content-Type', prometheusRegister.contentType);
             res.end(prometheusRegister.metrics());
         });
     }