API and process monitoring with Prometheus for Node.js micro-service

Usage no npm install needed!

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Prometheus API Monitoring

NPM Version NPM Downloads Build Status Test Coverage Known Vulnerabilities Apache 2.0 License


API and process monitoring with Prometheus for Node.js micro-service

Note: Prometheus (prom-client) is a peer dependency since 1.x version


  • Collect API metrics for each call
    • Response time in seconds
    • Request size in bytes
    • Response size in bytes
    • Add prefix to metrics names - custom or project name
    • Exclude specific routes from being collect
    • Number of open connections to the server
  • Process Metrics as recommended by Prometheus itself
  • Endpoint to retrieve the metrics - used for Prometheus scraping
    • Prometheus format
    • JSON format (${path}.json)
  • Support custom metrics
  • Http function to collect request.js HTTP request duration


const apiMetrics = require('prometheus-api-metrics');


Option Type Description Default Value
metricsPath String Path to access the metrics /metrics
defaultMetricsInterval Number Interval to collect the process metrics in milliseconds 10000
durationBuckets Array<Number> Buckets for response time in seconds [0.001, 0.005, 0.015, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5]
requestSizeBuckets Array<Number> Buckets for request size in bytes [5, 10, 25, 50, 100, 250, 500, 1000, 2500, 5000, 10000]
responseSizeBuckets Array<Number> Buckets for response size in bytes [5, 10, 25, 50, 100, 250, 500, 1000, 2500, 5000, 10000]
useUniqueHistogramName Boolean Add to metrics names the project name as a prefix (from package.json) false
metricsPrefix String A custom metrics names prefix, the package will add underscore between your prefix to the metric name
excludeRoutes Array<String> Array of routes to exclude. Routes should be in your framework syntax
includeQueryParams Boolean Indicate if to include query params in route, the query parameters will be sorted in order to eliminate the number of unique labels false
additionalLabels Array<String> Indicating custom labels that can be included on each http_* metric. Use in conjunction with extractAdditionalLabelValuesFn.
extractAdditionalLabelValuesFn Function A function that can be use to generate the value of custom labels for each of the http_* metrics. When using koa, the function takes ctx, when using express, it takes req, res as arguments

Access the metrics

To get the metrics in Prometheus format use:

curl http[s]://<host>:[port]/metrics

To get the metrics in JSON format use:

curl http[s]://<host>:[port]/metrics.json


  1. If you pass to the middleware the metricsPath option the path will be the one that you chose.

  2. If you are using express framework and no route was found for the request (e.g: 404 status code), the request will not be collected. that's because we'll risk memory leak since the route is not a pattern but a hardcoded string.

Custom Metrics

You can expand the API metrics with more metrics that you would like to expose. All you have to do is:

Require prometheus client

const Prometheus = require('prom-client');

Create new metric from the kind that you like

const checkoutsTotal = new Prometheus.Counter({
  name: 'checkouts_total',
  help: 'Total number of checkouts',
  labelNames: ['payment_method']

Update it:{
  payment_method: paymentMethod

The custom metrics will be exposed under the same endpoint as the API metrics.

For more info about the Node.js Prometheus client you can read here


This will work only if you use the default Prometheus registry - do not use new Prometheus.Registry()

Additional Metric Labels

You can define additional metric labels by using additionalLabels and extractAdditionalLabelValuesFn options.

For instance:

const apiMetrics = require('prometheus-api-metrics');
  additionalLabels: ['customer', 'cluster'],
  extractAdditionalLabelValuesFn: (req, res) => {
      const { headers } = req.headers;
      return {
        customer: headers['x-custom-header-customer'],
        cluster: headers['x-custom-header-cluster']

Request.js HTTP request duration collector

This feature enables you to easily process the result of Request.js timings feature.



You can choose to initialized this functionality as a Class or not


const HttpMetricsCollector = require('prometheus-api-metrics').HttpMetricsCollector;
const collector = new HttpMetricsCollector();


const HttpMetricsCollector = require('prometheus-api-metrics').HttpMetricsCollector;


  • durationBuckets - the histogram buckets for request duration.
  • countClientErrors - Boolean that indicates whether to collect client errors as Counter, this counter will have target and error code labels.
  • useUniqueHistogramName - Add to metrics names the project name as a prefix (from package.json)
  • prefix - A custom metrics names prefix, the package will add underscore between your prefix to the metric name.

For Example:


request({ url: '', time: true }, (err, response) => {
    Collector.collect(err || response);


return requestPromise({ method: 'POST', url: '', route: 'v2/:id', time: true, resolveWithFullResponse: true }).then((response) => {
}).catch((error) => {


  1. In order to use this feature you must use { time: true } as part of your request configuration and then pass to the collector the response or error you got.
  2. In order to use the timing feature in request-promise/request-promise-native you must also use resolveWithFullResponse: true
  3. Override - you can override the route and target attribute instead of taking them from the request object. In order to do that you should set a metrics object on your request with those attribute:
request({ method: 'POST', url: '', metrics: { target: '', route: 'v2/:id' }, time: true }, (err, response) => {...};


const axios = require('axios');
const axiosTime = require('axios-time');


try {
    const response = await axios({ baseURL: '', method: 'get', url: '/' });
} catch (error) {


  • In order to collect metrics from axios client the axios-time package is required.

Usage in koa

This package supports koa server that uses koa-router and koa-bodyparser

const { koaMiddleware } = require('prometheus-api-metrics')



npm test

Prometheus Examples Queries


(sum(rate(http_request_duration_seconds_bucket{<SERVICE_LABLE_FIELD>="<SERVICE_LABEL>">, route="<ROUTE_NAME>", le="0.05"}[10m])) by (<SERVICE_LABLE_FIELD>) + sum(rate(http_request_duration_seconds_bucket{<SERVICE_LABLE_FIELD>="<SERVICE_LABEL>", route="<ROUTE_NAME>", le="0.1"}[10m])) by (<SERVICE_LABLE_FIELD>)) / 2 / sum(rate(http_request_duration_seconds_count{<SERVICE_LABLE_FIELD>="<SERVICE_LABEL>", route="<ROUTE_NAME>"}[10m])) by (<SERVICE_LABLE_FIELD>)

95th Response Time by specific route and status code

histogram_quantile(0.95, sum(rate(http_request_duration_seconds_bucket{<SERVICE_LABLE_FIELD>="<SERVICE_LABEL>", route="<ROUTE_NAME>", code="200"}[10m])) by (le))

Median Response Time Overall

histogram_quantile(0.50, sum(rate(http_request_duration_seconds_bucket{<SERVICE_LABLE_FIELD>="<SERVICE_LABEL>"}[10m])) by (le))

Median Request Size Overall

histogram_quantile(0.50, sum(rate(http_request_size_bytes_bucket{<SERVICE_LABLE_FIELD>="<SERVICE_LABEL>"}[10m])) by (le))

Median Response Size Overall

histogram_quantile(0.50, sum(rate(http_response_size_bytes_bucket{<SERVICE_LABLE_FIELD>="<SERVICE_LABEL>"}[10m])) by (le))

Avarage Memory Usage - All services

avg(nodejs_external_memory_bytes / 1024 / 1024) by (<SERVICE_LABLE_FIELD)

Avarage Eventloop Latency - All services

avg(nodejs_eventloop_lag_seconds) by (<SERVICE_LABLE_FIELD)