@loopback/metrics NPM

@loopback/metrics

This module contains a component that reports metrics of Node.js, LoopBack framework, and your application to Prometheus.

Stability: ⚠️Experimental⚠️

Experimental packages provide early access to advanced or experimental functionality to get community feedback. Such modules are published to npm using 0.x.y versions. Their APIs and functionality may be subject to breaking changes in future releases.

Installation

npm install --save @loopback/metrics

Basic use

The component should be loaded in the constructor of your custom Application class.

Start by importing the component class:

import {MetricsComponent} from '@loopback/metrics';

In the constructor, add the component to your application:

this.component(MetricsComponent);

By default, Metrics route is mounted at /metrics. This path can be customized via Metrics configuration as follows:

this.configure(MetricsBindings.COMPONENT).to({
  endpoint: {
    basePath: '/metrics',
  },
  defaultMetrics: {
    timeout: 5000,
  },
  defaultLabels: {
    service: 'api',
    version: '1.0.0',
  },
});

{% include note.html content="this.configure() must be called before this.component() to take effect." %}

It also has to be noted, that by default the OpenAPI spec is disabled and therefore the metrics endpoint will not be visible in the API explorer. The spec can be enabled by setting openApiSpec to true.

this.configure(MetricsBindings.COMPONENT).to({
  openApiSpec: true,
});

Metrics Collected

There are three types of metrics being collected by this component:

Node.js metrics - built-in by https://github.com/siimon/prom-client
LoopBack method invocations - built-in by this module using an interceptor
Metrics by the application code or other modules - instrumentations are required

Pull vs Push

Prometheus supports two modes to collect metrics:

pull - scraping from metrics http endpoint exposed by the system being monitored. This is the usual mode of operation. See Why do you pull rather than push?
push - pushing metrics from the system being monitored to a push gateway. Generally used for ephemeral jobs - see When to use the Pushgateway

Try it out

git clone https://github.com/loopbackio/loopback-next
npm install
npm run build
cd examples/metrics-prometheus
npm run demo

Open http://localhost:9090 to load Prometheus web UI.

/metrics endpoint

http://localhost:3000/metrics returns metrics in plain text format. It includes information for the Node.js process as well as LoopBack method invocations.