vestfold-metrics

This repository is a wrapper on the prom-client library to provide easier interaction with Prometheus metrics in a Node.js application.

Installation

npm install vestfold-metrics

Usage

All metrics can take optional labels as an array of string in the format ...[name, value]

If a metric is created with a set of labels, all future interactions with that metric must use the same set of labels.

Counter metric

See the prom-client documentation for counter details.

import { count, countInc } from 'vestfold-metrics'

// Create and increment a counter without labels - Will result in a counter named 'my_counter' with the value of 1
count('my_counter', 'This is my counter')

// Increment the same counter again - Will reuse the counter named 'my_counter' and the value is now 2
count('my_counter', 'This is my counter')

// Create and increment a counter with labels - Will result in a counter named 'my_counter_label' with the value of 1 and label 'result' with value 'success'
count('my_counter_label', 'This is my counter with label', ['result', 'success'])

// Increment the same counter again - Will reuse the counter named 'my_counter_label' and the value is now 2 and label 'result' with value 'success'
count('my_counter_label', 'This is my counter with label', ['result', 'success'])



// Create and increment a counter with specific increment value without labels - Will result in a counter named 'my_counter_inc' with the value of 19
countInc('my_counter_inc', 'This is my counter', 19)

// Increment the same counter again with specific increment value - Will reuse the counter named 'my_counter_inc' and the value is now 40
countInc('my_counter_inc', 'This is my counter', 21)

// Create and increment a counter with specific increment value with labels - Will result in a counter named 'my_counter_inc_label' with the value of 19 and label 'result' with value 'success'
countInc('my_counter_inc_label', 'This is my counter with label', 19, ['result', 'success'])

// Increment the same counter again with specific increment value - Will reuse the counter named 'my_counter_inc_label' and the value is now 40 and label 'result' with value 'success'
countInc('my_counter_inc_label', 'This is my counter with label', 21, ['result', 'success'])

Gauge metric

See the prom-client documentation for gauge details.

import { gauge } from 'vestfold-metrics'

// Create and set a gauge without labels - Will result in a gauge named 'my_gauge' with the value of 10
gauge('my_gauge', 'This is my gauge', 10)

// Set the same gauge again - Will reuse the gauge named 'my_gauge' and the value is now 5
gauge('my_gauge', 'This is my gauge', 5)

// Create and set a gauge with labels - Will result in a gauge named 'my_gauge_label' with the value of 15 and label 'result' with value 'success'
gauge('my_gauge_label', 'This is my gauge with label', 15, ['result', 'success'])

// Set the same gauge again - Will reuse the gauge named 'my_gauge_label' and the value is now 8 and label 'result' with value 'success'
gauge('my_gauge_label', 'This is my gauge with label', 8 ['result', 'success'])

Metrics endpoint

Expose your metrics to Prometheus by creating an HTTP endpoint in your Node.js application. This endpoint should return the metrics in the Prometheus exposition format.

Example for Azure Functions:

import { app, HttpRequest, HttpResponseInit, InvocationContext } from '@azure/functions'
import { register } from 'vestfold-metrics'

export async function metrics(_: HttpRequest, __: InvocationContext): Promise<HttpResponseInit> {
  return {
    status: 200,
    headers: { 'Content-Type': register.contentType },
    body: await register.metrics()
  }
}

app.get('metrics', {
  authLevel: 'function',
  handler: metrics
})

Example for Express

import express from 'express'
import { register } from 'vestfold-metrics'

const app = express()

app.get('/metrics', async (_req, res) => {
  res.set('Content-Type', register.contentType)
  res.end(await register.metrics())
})

app.listen(3000, () => {
  console.log('Server listening on port 3000')
})