util.js

/**
 * Newly added requires
 */
var Register = require('prom-client').register;
var Counter = require('prom-client').Counter;
var Histogram = require('prom-client').Histogram;
var Summary = require('prom-client').Summary;
var Gauge = require('prom-client').Gauge;
var ResponseTime = require('response-time');
let appVersion = process.env.APP_VERSION;
let appCommit = process.env.APP_COMMIT;
let appBranch = process.env.APP_BRANCH;
let appTime = process.env.APP_TIME;

if (!appVersion) {
   appVersion = 'undefinded';
   console.log(`Application version: ${appVersion}`);
}

if (!appCommit) {
   appCommit = 'undefinded';
   console.log(`Application commit: ${appCommit}`);
}

if (!appBranch) {
   appBranch = 'undefinded';
   console.log(`Application branch: ${appBranch}`);
}

if (!appTime) {
   appTime = 'undefinded';
   console.log(`Application branch: ${appTime}`);
}

var version = appVersion;
var commit = appCommit;
var branch = appBranch;
var buildTime = appTime;


/**
 * A Prometheus counter that counts the invocations of the different HTTP verbs
 * e.g. a GET and a POST call will be counted as 2 different calls
 */
module.exports.numOfRequests = numOfRequests = new Counter({  
    name: 'numOfRequests',
    help: 'Number of requests made',
    labelNames: ['method']
});

/**
 * A Prometheus counter that counts the invocations with different paths
 * e.g. /foo and /bar will be counted as 2 different paths
 */
module.exports.pathsTaken = pathsTaken = new Counter({  
    name: 'pathsTaken',
    help: 'Paths taken in the app',
    labelNames: ['path']
});


module.exports.pathsTaken = pathsAdmin = new Gauge({
      name: `build_info`,
      help: `A metric with a constant 1 value labeled by version, revision, platform, nodeVersion, os from which was built`,
      labelNames: [
        'version',
        'commit',
        'branch',
        'buildTime',
      ]
});

pathsAdmin.set(
      {
        version,
        commit,
        branch,
        buildTime,
      },
      1,
);

/**
 * A Prometheus summary to record the HTTP method, path, response code and response time
 */
module.exports.responses = responses = new Summary({  
    name: 'responses',
    help: 'Response time in millis',
    labelNames: ['method', 'path', 'status']
});

/**
 * This funtion will start the collection of metrics and should be called from within in the main js file
 */
module.exports.startCollection = function () {  
    console.log(`Starting the collection of metrics, the metrics are available on /metrics`);
    require('prom-client').collectDefaultMetrics();
};

/**
 * This function increments the counters that are executed on the request side of an invocation
 * Currently it increments the counters for numOfPaths and pathsTaken
 */
module.exports.requestCounters = function (req, res, next) {  
    if (req.path != '/metrics') {
        numOfRequests.inc({ method: req.method });
        pathsTaken.inc({ path: req.path });
    }
    next();
}

/**
 * This function increments the counters that are executed on the response side of an invocation
 * Currently it updates the responses summary
 */
module.exports.responseCounters = ResponseTime(function (req, res, time) {  
    if(req.url != '/metrics') {
        responses.labels(req.method, req.url, res.statusCode).observe(time);
    }
})

/**
 * In order to have Prometheus get the data from this app a specific URL is registered
 */
module.exports.injectMetricsRoute = function (App) {  
    App.get('/metrics', (req, res) => {
        res.set('Content-Type', Register.contentType);
        res.end(Register.metrics());
    });
};