feat(metrics): added /metrics endpoint. Fixes MEMB-604

lib/helpers.js

@@ -62,6 +62,54 @@ exports.flattenObject = (obj, prefix = '') => {
     }, {});
 };
 
+// A helper to count objects by a set of fields.
+exports.countByFields = (array, keys) => {
+    const reduceFunc = (acc, val) => {
+        // finding element with such keys values
+        const accElement = acc.find((elementInAcc) => {
+            for (const key of keys) {
+                if (elementInAcc[key] !== val[key]) {
+                    return false;
+                }
+            }
+
+            return true;
+        });
+
+        // if found, increment value, if not, adding another element
+        // to result array.
+        if (accElement) {
+            accElement.value += 1;
+        } else {
+            const elt = { value: 1 };
+            for (const key of keys) {
+                elt[key] = val[key];
+            }
+            acc.push(elt);
+        }
+
+        return acc;
+    };
+
+    return array.reduce(reduceFunc, []);
+};
+
+// A helper to add data to gauge Prometheus metric.
+exports.addGaugeData = (gauge, array) => {
+    // reset gauge...
+    gauge.reset();
+
+    // and set it with values
+    for (const element of array) {
+        const {
+            value,
+            ...data
+        } = element;
+
+        gauge.set(data, value);
+    }
+};
+
 // A helper uset to pretty-format values.
 exports.beautify = (value) => {
     // If it's boolean, display it as Yes/No instead of true/false

lib/metrics.js

@@ -0,0 +1,52 @@
+const {
+    Gauge,
+    register
+} = require('prom-client');
+
+const {
+    Event,
+    Application
+} = require('../models');
+const helpers = require('./helpers');
+
+const createGauge = (name, help, labels = []) => new Gauge({
+    name,
+    help,
+    labelNames: labels
+});
+
+const gaugesList = {
+    eventsTotal: createGauge('events_total', 'Total amount of events'),
+    eventsByType: createGauge('events_by_type', 'Amount of events by type', ['type']),
+    eventsByTypeAndStatus: createGauge('events_by_type_and_status', 'Amount of events by type and status', ['type', 'status']),
+    applicationsTotal: createGauge('applications_total', 'Total amount of applications'),
+    applicationsByEvent: createGauge('applications_by_event', 'Amount of applications by event', ['event_name']),
+    applicationsByEventAndStatus: createGauge('applications_by_event_and_status', 'Amount of applications by event and status', ['event_name', 'status']),
+    applicationsByEventAndBody: createGauge('applications_by_event_and_body', 'Amount of applications by event and body', ['event_name', 'body_name']),
+};
+
+exports.getMetrics = async (req, res) => {
+    let [
+        events,
+        applications,
+    ] = await Promise.all([
+        Event.findAll(),
+        Application.findAll({ include: [Event] }),
+    ]);
+
+    events = events.map((event) => event.toJSON());
+    applications = applications.map((application) => Object.assign(application.toJSON(), { event_name: application.event.name }));
+
+    // setting gauges with real data
+    helpers.addGaugeData(gaugesList.eventsTotal, helpers.countByFields(events, []));
+    helpers.addGaugeData(gaugesList.eventsByType, helpers.countByFields(events, ['type']));
+    helpers.addGaugeData(gaugesList.eventsByTypeAndStatus, helpers.countByFields(events, ['type', 'status']));
+
+    helpers.addGaugeData(gaugesList.applicationsTotal, helpers.countByFields(applications, []));
+    helpers.addGaugeData(gaugesList.applicationsByEvent, helpers.countByFields(applications, ['event_name']));
+    helpers.addGaugeData(gaugesList.applicationsByEventAndBody, helpers.countByFields(applications, ['event_name', 'body_name']));
+    helpers.addGaugeData(gaugesList.applicationsByEventAndStatus, helpers.countByFields(applications, ['event_name', 'status']));
+
+    res.set('Content-Type', register.contentType);
+    res.end(register.metrics());
+};

lib/server.js

@@ -11,6 +11,7 @@ const applications = require('./applications'); // API middlewares for applicati
 const imageserv = require('./imageserv');
 const log = require('./logger');
 const middlewares = require('./middlewares');
+const metrics = require('./metrics');
 const config = require('../config');
 
 const EventsRouter = router({ mergeParams: true });
@@ -39,6 +40,7 @@ process.on('unhandledRejection', (err) => {
 ImagesRouter.use(express.static(config.media_dir)); // Serving images.
 
 GeneralRouter.get('/healthcheck', middlewares.healthcheck);
+GeneralRouter.get('/metrics', metrics.getMetrics);
 GeneralRouter.use(middlewares.authenticateUser);
 
 GeneralRouter.get('/', events.listEvents);

package.json

@@ -56,6 +56,7 @@
     "node-schedule": "^1.3.2",
     "node-xlsx": "^0.15.0",
     "pg": "^7.12.1",
+    "prom-client": "^11.5.3",
     "read-chunk": "^3.2.0",
     "request": "^2.88.0",
     "request-promise-native": "^1.0.7",

test/api/metrics.test.js

@@ -0,0 +1,32 @@
+const { startServer, stopServer } = require('../../lib/server.js');
+const { request } = require('../scripts/helpers');
+const generator = require('../scripts/generator');
+const mock = require('../scripts/mock-core-registry');
+
+describe('Metrics requests', () => {
+    beforeEach(async () => {
+        mock.mockAll();
+        await startServer();
+    });
+
+    afterEach(async () => {
+        await stopServer();
+        mock.cleanAll();
+    });
+
+    test('should return data correctly', async () => {
+        const event = await generator.createEvent({});
+        await generator.createApplication({ user_id: 1, status: 'accepted' }, event);
+        await generator.createApplication({ user_id: 2, status: 'accepted' }, event);
+        await generator.createApplication({ user_id: 3, status: 'pending' }, event);
+
+
+        const res = await request({
+            uri: '/metrics',
+            method: 'GET',
+            json: false
+        });
+
+        expect(res.statusCode).toEqual(200);
+    });
+});