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jochen-schweizer / express-prom-bundle

express middleware with standard prometheus metrics in one bundle
MIT License
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express-middleware metrics npm-package

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express prometheus bundle

Express middleware with popular prometheus metrics in one bundle. It's also compatible with koa v1 and v2 (see below).

This library uses prom-client v15+ as a peer dependency. See: https://github.com/siimon/prom-client

If you need a support for older versions of prom-client (v12-v14), downgrade to express-prom-bundle v6.6.0

Included metrics:

Install

npm install prom-client express-prom-bundle

Sample Usage

const promBundle = require("express-prom-bundle");
const app = require("express")();
const metricsMiddleware = promBundle({includeMethod: true});

app.use(metricsMiddleware);
app.use(/* your middleware */);
app.listen(3000);

ALERT!

The order in which the routes are registered is important, since only the routes registered after the express-prom-bundle will be measured

You can use this to your advantage to bypass some of the routes. See the example below.

Options

Which labels to include in http_request_duration_seconds metric:

metricType option

Two metric types are supported for http_request_duration_seconds metric:

Additional options for histogram:

Additional options for summary:

Transformation callbacks

Other options

More details on includePath option

Let's say you want to have latency statistics by URL path, e.g. separate metrics for /my-app/user/, /products/by-category etc.

Just taking req.path as a label value won't work as IDs are often part of the URL, like /user/12352/profile. So what we actually need is a path template. The module tries to figure out what parts of the path are values or IDs, and what is an actual path. The example mentioned before would be normalized to /user/#val/profile and that will become the value for the label. These conversions are handled by normalizePath function.

You can extend this magical behavior by providing additional RegExp rules to be performed, or override normalizePath with your own function.

Example 1 (add custom RegExp):

app.use(promBundle({
  normalizePath: [
    // collect paths like "/customer/johnbobson" as just one "/custom/#name"
    ['^/customer/.*', '/customer/#name'],

    // collect paths like "/bobjohnson/order-list" as just one "/#name/order-list"
    ['^.*/order-list', '/#name/order-list']
  ],
  urlValueParser: {
    minHexLength: 5,
    extraMasks: [
      'ORD[0-9]{5,}' // replace strings like ORD1243423, ORD673562 as #val
    ]
  }
}));

Example 2 (override normalizePath function):

app.use(promBundle(/* options? */));

// let's reuse the existing one and just add some
// functionality on top
const originalNormalize = promBundle.normalizePath;
promBundle.normalizePath = (req, opts) => {
  const path = originalNormalize(req, opts);
  // count all docs as one path, but /docs/login as a separate one
  return (path.match(/^\/docs/) && !path.match(/^\/login/)) ? '/docs/*' : path;
};

For more details:

Example 3 (return express route definition):

app.use(promBundle(/* options? */));

promBundle.normalizePath = (req, opts) => {
  // Return the path of the express route (i.e. /v1/user/:id or /v1/timer/automated/:userid/:timerid")
  return req.route?.path ?? "NULL";
};

express example

setup std. metrics but exclude up-metric:

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

// calls to this route will not appear in metrics
// because it's applied before promBundle
app.get("/status", (req, res) => res.send("i am healthy"));

// register metrics collection for all routes
// ... except those starting with /foo
app.use("/((?!foo))*", promBundle({includePath: true}));

// this call will NOT appear in metrics,
// because express will skip the metrics middleware
app.get("/foo", (req, res) => res.send("bar"));

// calls to this route will appear in metrics
app.get("/hello", (req, res) => res.send("ok"));

app.listen(3000);

See an advanced example on github

koa v2 example

const promBundle = require("express-prom-bundle");
const Koa = require("koa");
const c2k = require("koa-connect");
const metricsMiddleware = promBundle({/* options */ });

const app = new Koa();

app.use(c2k(metricsMiddleware));
app.use(/* your middleware */);
app.listen(3000);

using with cluster

You'll need to use an additional clusterMetrics() middleware.

In the example below the master process will expose an API with a single endpoint /metrics which returns an aggregate of all metrics from all the workers.

const cluster = require('cluster');
const promBundle = require('express-prom-bundle');
const promClient = require('prom-client');
const numCPUs = Math.max(2, require('os').cpus().length);
const express = require('express');

if (cluster.isMaster) {
    for (let i = 1; i < numCPUs; i++) {
        cluster.fork();
    }

    const metricsApp = express();
    metricsApp.use('/metrics', promBundle.clusterMetrics());
    metricsApp.listen(9999);

    console.log('cluster metrics listening on 9999');
    console.log('call localhost:9999/metrics for aggregated metrics');
} else {
    new promClient.AggregatorRegistry();
    const app = express();
    app.use(promBundle({
        autoregister: false, // disable /metrics for single workers
        includeMethod: true
    }));
    app.use((req, res) => res.send(`hello from pid ${process.pid}\n`));
    app.listen(3000);
    console.log(`worker ${process.pid} listening on 3000`);
}

using with kraken.js

Here is meddleware config sample, which can be used in a standard kraken.js application. In this case the stats for URI paths and HTTP methods are collected separately, while replacing all HEX values starting from 5 characters and all IP addresses in the path as #val.

{
  "middleware": {
    "expressPromBundle": {
      "route": "/((?!status|favicon.ico|robots.txt))*",
      "priority": 0,
      "module": {
        "name": "express-prom-bundle",
        "arguments": [
          {
            "includeMethod": true,
            "includePath": true,
            "buckets": [0.1, 1, 5],
            "promClient": {
              "collectDefaultMetrics": {
              }
            },
            "urlValueParser": {
              "minHexLength": 5,
              "extraMasks": [
                "^[0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+$"
              ]
            }
          }
        ]
      }
    }
  }
}

License

MIT