Add metrics for P5

bulletin-board-app/package.json

@@ -13,7 +13,8 @@
     "vue": "^1.0.10",
     "vue-resource": "^0.1.17",
     "tedious": "^2.0.1",
-    "sequelize": "^4.20.1"
+    "sequelize": "^4.20.1",
+    "prom-client": "^10.2.2"
   },
   "devDependencies": {
     "body-parser": "^1.14.1",

bulletin-board-app/server.js

@@ -3,6 +3,7 @@ var express        = require('express'),
     methodOverride = require('method-override'),
     errorHandler   = require('errorhandler'),
     morgan         = require('morgan'),
+    prometheus     = require('prom-client'),
     routes         = require('./backend'),
     api            = require('./backend/api');
 
@@ -29,10 +30,42 @@ if ('production' == app.get('env')) {
   app.use(errorHandler());
 }
 
+// counter for Prometheus:
+const httpRequestDurationMicroseconds = new prometheus.Histogram({
+  name: 'http_request_duration_ms',
+  help: 'Duration of HTTP requests in ms',
+  labelNames: ['method', 'route', 'code'],
+  buckets: [0.10, 5, 15, 50, 100, 200, 300, 400, 500]  // buckets for response time from 0.1ms to 500ms
+})
+
+// record timestamp before request handler:
+app.use((req, res, next) => {
+  res.locals.startEpoch = Date.now()
+  next()
+})
+
 app.get('/', routes.index);
 app.get('/api/events', api.events);
 app.post('/api/events', api.event);
-app.delete('/api/events/:eventId', api.event)
+app.delete('/api/events/:eventId', api.event);
+
+app.get('/metrics', (req, res) => {
+  res.set('Content-Type', prometheus.register.contentType)
+  res.end(prometheus.register.metrics())
+})
+
+// set response duration after handler:
+app.use((req, res, next) => {
+  const responseTimeInMs = Date.now() - res.locals.startEpoch
+
+  httpRequestDurationMicroseconds
+    .labels(req.method, req.path, res.statusCode)
+    .observe(responseTimeInMs)
+
+  next()
+})
+
+prometheus.collectDefaultMetrics();
 
 app.listen(8080);
 console.log('Magic happens on port 8080...');