Question: How do I configure a different port for the metrics

[poteirard]

Hello ! First of all thank you for you amazing work on this repo :)

In my company we are using Prometheus for all the java projects and I wanted to achieve the same for our node servers as well.

All the endpoints of metrics however has to be in a specific port (different from the app server). Something like my-url.com:9000/metrics.

Is it possible to achieve that with this repo?

Thank you :)

[goooseman]

It is not so obvious, because this middleware attaches to express, which is listening on one of the ports. Middleware can not expose itself to a different port. This can not be solved by extending the API of this library, but can be done on the integration side in your code.

To solve this issue, we need one more express app, which has only /metrics endpoint. But we need to register statistics from our main express app. In the end I came up with the following:

const express = require("express");
const promBundle = require("express-prom-bundle");

const metricsRequestMiddleware = promBundle({
  includePath: true,
  includeMethod: true,
  autoregister: false, // Do not register /metrics
  promClient: {
    collectDefaultMetrics: {
    },
  },
});
const { promClient, metricsMiddleware } = metricsRequestMiddleware;
// promClient here is the prom-client object 

// Metrics app to expose /metrics endpoint
const metricsApp = express();
metricsApp.use(metricsMiddleware);

module.exports = { metricsRequestMiddleware, metricsApp };

const express = require("express");
const app = express();
const { metricsRequestMiddleware } = require("@server/app/metrics");

// We are using metricsRequestMiddleware which register statistics from main express app
app.use(metricsRequestMiddleware);

const app = require("./server/app");
const { metricsApp } = require("./server/app/metrics");

const server = http.createServer(app); // Main server
const metricsServer = http.createServer(metricsApp); // Metrics server
server.listen(5000);
metricsServer.listen(9090);

[poteirard]

It works like a charm. Thanks a lot for the code and the comments !

[shaharsol]

@goooseman @poteirard just implemented this solution in my app and found out that indeed I can now access the /metrics endpoint on port 9090, however I can still access the metrics via the main app port i.e localhost:3000/metrics.
Am I missing something? Is there anyway to limit access to the metrics endpoint on the main app port?

Edit: I kinda work around this like so:

    app.use('/metrics', (req, res) => {
        res.send(401);
    });
    app.use(metricsRequestMiddleware);

But it feels hacky to me...

[shaharsol]

My other issue with that solution is that I can't seem to use the ordering of the uses to determine which route will be measured and which will not. Everything is included regardless of where I use the metricsRequestMiddleware.

[lehno]

Same problem as you @shaharsol

[elaijuh]

express-prom-bundle/src/index.js

Line 132 in 23cedb9

if (opts.autoregister && path.match(metricsMatch)) {

@shaharsol

[nasonfish]

Here's a solution that seems to work for me.

const app = express();
const metricsApp = express();

const metricsMiddleware = promBundle({
    includeMethod: true,
    includePath: true,
    autoregister: false,
});

app.use(metricsMiddleware);

// app.use(.....)
app.listen(config.PORT, () => {
    console.log('Server listening on port', config.PORT);
});

metricsApp.use(metricsMiddleware.metricsMiddleware);

metricsApp.listen(config.METRICS_PORT, () => {
    console.log('Metrics listening on port', config.METRICS_PORT);
});

It appears to register the metrics endpoint correctly in the metrics server, while collecting the actual metrics from the app.

[ath88]

I added an option that makes this far easier. Check out #101.