express-prometheus-middleware
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1.2.0 • Public • Published

Express Prometheus Middleware

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This is a middleware for express servers, that expose metrics for prometheus.

The metrics exposed allows to calculate common RED (Request, Error rate, Duration of requests), and USE (Utilisation, Error rate, and Saturation), metrics

Install

yarn add express-prometheus-middleware
# or
npm i --save express-prometheus-middleware

Usage

Options

Name Description Default
metricsPath Url route that will expose the metrics for scraping. /metrics
metricsApp Express app that will expose metrics endpoint, if an app is provided, use it, instead of instantiating a new one null
collectDefaultMetrics Whether or not to collect prom-client default metrics. These metrics are usefull for collecting saturation metrics, for example. true
collectGCMetrics Whether or not to collect garbage collection metrics via module prometheus-gc-stats. Dependency prometheus-gc-stats is marked as optional, hence if this option is set to true but npm/yarn could not install the dependency, no garbage collection metric will be collected. false
requestDurationBuckets Buckets for the request duration metrics (in seconds) histogram Uses prom-client utility: Prometheus.exponentialBuckets(0.05, 1.75, 8)
requestLengthBuckets Buckets for the request length metrics (in bytes) histogram no buckets (The request length metrics are not collected): []
responseLengthBuckets Buckets for the response length metrics (in bytes) histogram no buckets (The response length metrics are not collected) []
extraMasks Optional, list of regexes to be used as argument to url-value-parser, this will cause extra route params, to be replaced with a #val placeholder. no extra masks: []
authenticate Optional authentication callback, the function should receive as argument, the req object and return truthy for sucessfull authentication, or falsy, otherwise. This option supports Promise results. null
prefix Optional prefix for the metrics name no prefix added
customLabels Optional Array containing extra labels, used together with transformLabels no extra labels: []
transformLabels Optional function(labels, req, res) adds to the labels object dynamic values for each label in customLabels null
normalizeStatus Optional parameter to disable normalization of the status code. Example of normalized and non-normalized status code respectively: 4xx and 422. true

Example

const express = require('express');
const promMid = require('express-prometheus-middleware');
const app = express();

const PORT = 9091;
app.use(promMid({
  metricsPath: '/metrics',
  collectDefaultMetrics: true,
  requestDurationBuckets: [0.1, 0.5, 1, 1.5],
  requestLengthBuckets: [512, 1024, 5120, 10240, 51200, 102400],
  responseLengthBuckets: [512, 1024, 5120, 10240, 51200, 102400],
  /**
   * Uncomenting the `authenticate` callback will make the `metricsPath` route
   * require authentication. This authentication callback can make a simple
   * basic auth test, or even query a remote server to validate access.
   * To access /metrics you could do:
   * curl -X GET user:password@localhost:9091/metrics
   */
  // authenticate: req => req.headers.authorization === 'Basic dXNlcjpwYXNzd29yZA==',
  /**
   * Uncommenting the `extraMasks` config will use the list of regexes to
   * reformat URL path names and replace the values found with a placeholder value
  */
  // extraMasks: [/..:..:..:..:..:../],
  /**
   * The prefix option will cause all metrics to have the given prefix.
   * E.g.: `app_prefix_http_requests_total`
   */
  // prefix: 'app_prefix_',
  /**
   * Can add custom labels with customLabels and transformLabels options
   */
  // customLabels: ['contentType'],
  // transformLabels(labels, req) {
  //   // eslint-disable-next-line no-param-reassign
  //   labels.contentType = req.headers['content-type'];
  // },
}));

// curl -X GET localhost:9091/hello?name=Chuck%20Norris
app.get('/hello', (req, res) => {
  console.log('GET /hello');
  const { name = 'Anon' } = req.query;
  res.json({ message: `Hello, ${name}!` });
});

app.listen(PORT, () => {
  console.log(`Example api is listening on http://localhost:${PORT}`);
});

Metrics exposed

  • Default metrics from prom-client
  • http_requests_total: Counter for total requests received, has labels route, method, status
  • http_request_duration_seconds: - Duration of HTTP requests in seconds, has labels route, method, status

The labels route and status are normalized:

  • route: will normalize id like route params
  • status: will normalize to status code family groups, like 2XX or 4XX.

Example prometheus queries

In the examples below, Suppose you tagged your application as "myapp", in the prometheus scrapping config.

Running instances

sum(up{app="myapp"})

Overall error rate

Rate of http status code 5XX responses

sum(rate(http_requests_total{status="5XX", app="myapp"}[5m]))

95% of requests served within seconds

histogram_quantile(0.95, sum(rate(http_request_duration_seconds_bucket{app="myapp"}[5m])) by (le))

95% of request length

histogram_quantile(0.95, sum(rate(http_request_length_bytes_bucket{app="myapp"}[5m])) by (le))

95% of response length

histogram_quantile(0.95, sum(rate(http_response_length_bytes_bucket{app="myapp"}[5m])) by (le))

Average response time in seconds

sum(rate(http_request_duration_seconds_sum{app="myapp"}[5m])) by (instance) / sum(rate(http_request_duration_seconds_count{app="myapp"}[5m])) by (instance)

Overall Request rate

sum(rate(http_requests_total{app="myapp"}[5m])) by (instance)

Request rate by route

In this example we are removing some health/status-check routes, replace them with your needs.

sum(rate(http_requests_total{app="myapp", route!~"/|/healthz"}[5m])) by (instance, route)

CPU usage

rate(process_cpu_system_seconds_total{app="myapp"}[5m])
rate(process_cpu_user_seconds_total{app="myapp"}[5m])

Memory usage

nodejs_heap_size_total_bytes{app="myapp"}
nodejs_heap_size_used_bytes{app="myapp"}

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npm i express-prometheus-middleware

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  • joao-fontenele