add prometheus exporter

package.json

@@ -10,6 +10,8 @@
   "repository": "https://github.com/nmasse-itix/OpenShift-Demo-NodeJS.git",
   "license": "MIT",
   "dependencies": {
-    "express": "latest"
+    "express": "latest",
+    "express-prom-bundle": "^6.5.0",
+    "prom-client": "^14.1.0"
   }
 }

server.js

@@ -1,3 +1,5 @@
+const client = require('prom-client')
+const promBundle = require("express-prom-bundle");
 var express = require("express");
 var app = express();
 var router = express.Router();
@@ -12,11 +14,32 @@ router.use(function (req,res,next) {
   console.log("%s %s => %i", req.method, req.originalUrl, res.statusCode);
 });
 
+// Prometheus exporter
+const registry = new client.Registry()
+const metricsMiddleware = promBundle({
+  includeMethod: true, 
+  includePath: true, 
+  includeStatusCode: true, 
+  includeUp: true,
+  customLabels: {app: 'openshift-demo-nodejs'},
+  promClient: {
+    collectDefaultMetrics: {
+    }
+  }
+});
+app.use(metricsMiddleware)
+const counter = new client.Counter({
+  name: 'openshift_demo_nodejs_calls',
+  help: 'Number of calls to the OpenShift-Demo-NodeJS',
+});
+registry.registerMetric(counter);
+
 router.get("/",function(req,res){
   res.sendFile(__dirname + '/views/index.html');
 });
 
 router.get("/info",function(req,res){
+  var status = 200;
   var response = {
     color: color,
     podName: process.env["HOSTNAME"],
@@ -24,22 +47,28 @@ router.get("/info",function(req,res){
   if (!ready) {
     response.color = "red";
     response.podName = "NOT READY";
+    status = 503;
+  } else {
+    counter.inc();
   }
   res.type('application/json')
      .header("Connection", "close")
      .header('Cache-Control', 'private, no-cache, no-store, must-revalidate')
      .header('Expires', '-1')
      .header('Pragma', 'no-cache')
+     .status(status)
      .send(JSON.stringify(response))
      .end();
 });
 
+// Liveness probe
 router.get("/health/live",function(req,res){
   res.type('application/json')
      .send({"alive": true})
      .end();
 });
 
+// Readiness probe
 router.get("/health/ready",function(req,res){
   if (ready) {
     res.type('application/json')