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Metrics instrumentation middleware for Express using prom-client
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README.md

Tricorder

Build Status Maintainability Test Coverage

Maintained by @jonnyarnold

Express middleware to provide basic metrics to Prometheus.

Prometheus is an open source monitoring solution that obtains metrics from servers by querying against the /metrics endpoint upon them.

Once instrumented, Tricorder automatically serves response duration metrics, nodejs system and garbage collection metrics on the /metrics endpoint ready to be consumed by Prometheus.

The inbuilt metrics are the basics you'll need to gain insight into your application and conforming to best practise.

Installation and Setup

npm install @trussle/tricorder --save

Installation into an express application;

const express = require("express");
const tricorder = require("@trussle/tricorder");
const app = express();

tricorder.instrument(app);

API

Tricorder exposes;

  • instrument(Express, options) - used to add metrics to your express server
  • client() - expose prom-client for use throughout your application

Options

The options object supports the following properties;

  • url - metrics url defaults to /metrics

Metrics

Http

  • http_requests_processing (gauge)
  • http_requests_total{labels} (counter)
  • http_request_duration_seconds{labels} (histogram) - count duration in prom-client default buckets

When labels are indicated as in included they will be as follows;

  • status: the http status code of the response, e.g. 200, 500
  • method: the http method of the request, e.g. put, post.
  • path: the path of the request. Note that /users/freddie is labelled /users/:id so not to create a large number of timeseries

System

These are metrics provided by prom-client that instrument the nodejs heap/rss usage and cpu usage etc.

Garbage Collection

These are metrics provided by prometheus-gc-stats that instrument the nodejs gc.

Why

The node/express eco-system already has a collection of Prometheus middleware implementations which don't all conform to best practise making metrics hard to consume and use to drive alerting.

Tricorder is designed to be the swiss army knife of metrics providing everything you need to get started in an easy to consume package.

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