PromeKoa

Instrument Koa app to Prometheus

PromeKoa automatically serves response duration metrics, plus nodejs system metrics on the /metrics path ready to be consumed by Prometheus.

Instrumentation

The following metrics are instrumented via /metrics path:

• http_request_duration_ms (histogram): a histogram metric used to count duration in buckets of sizes 100ms and 500ms. This can be used to calculate apdex using a response time threshold of 300ms.

Installation

> npm install promekoa --save

To instrument your Koa app you must import the promekoa lib and call instrument method with required params:

PromeKoa.instrument(app, router)

• The first argument represents an instance of Koa app. (*required)
• The second argument represents an instance of koa-router (*required)

See the example:

const Koa = require('koa');
const Router = require('koa-router')
const PromeKoa = require('promekoa');
const router = new Router()
const app = new Koa();

PromeKoa.instrument(app, router)

router
  .get('/hello', async (ctx, next) => {
    await new Promise((resolve, reject) => {
      setTimeout(() => {
        ctx.body = { "message": 'index route' }
        resolve();
      }, Math.round(Math.random() * 150));
    });
  })
  .get('/users', async (ctx, next) => {
    await new Promise((resolve, reject) => {
      setTimeout(() => {
        ctx.status = 500
        ctx.body = { "Error": 'Error to fetching users' }
        resolve();
      }, Math.round(Math.random() * 400));
    });
  })

app.use(router.routes())

app.listen(3001);