JonathanFaz/monitoring-prometheus-nodejs

counter

Counter is a monotonically increasing counter. It MUST NOT allow the value to decrease, however it MAY be reset to 0 (such as by server restart).

A counter MUST have the following methods:

• inc(): Increment the counter by 1
• inc(double v): Increment the counter by the given amount. MUST check that v >= 0. A counter is ENCOURAGED to have:

A way to count exceptions throw/raised in a given piece of code, and optionally only certain types of exceptions.

Counters MUST start at 0.

Gauge

Gauge represents a value that can go up and down.

A gauge MUST have the following methods:

• inc(): Increment the gauge by 1
• inc(double v): Increment the gauge by the given amount
• dec(): Decrement the gauge by 1
• dec(double v): Decrement the gauge by the given amount
• set(double v): Set the gauge to the given value
• Gauges MUST start at 0, you MAY offer a way for a given gauge to start at a different number.

A gauge SHOULD have the following methods:

set_to_current_time(): Set the gauge to the current unixtime in seconds. A gauge is ENCOURAGED to have:

A way to track in-progress requests in some piece of code/function. This is track_inprogress in Python.

A way to time a piece of code and set the gauge to its duration in seconds. This is useful for batch jobs. This is startTimer/setDuration in Java and the time() decorator/context manager in Python. This SHOULD match the pattern in Summary/Histogram (though set() rather than observe()).

Histogram

Histograms track sizes and frequency of events.

Configuration

The defaults buckets are intended to cover usual web/rpc requests, this can however be overriden.

const client = require('prom-client');
new client.Histogram({
  name: 'metric_name',
  help: 'metric_help',
  buckets: [0.1, 5, 15, 50, 100, 500]
});

You can include all label names as a property as well.

const client = require('prom-client');
new client.Histogram({
  name: 'metric_name',
  help: 'metric_help',
  labelNames: ['status_code'],
  buckets: [0.1, 5, 15, 50, 100, 500]
});

Examples

const client = require('prom-client');
const histogram = new client.Histogram({
  name: 'metric_name',
  help: 'metric_help'
});
histogram.observe(10); // Observe value in histogram

Utility to observe request durations

const end = histogram.startTimer();
xhrRequest(function(err, res) {
  end(); // Observes the value to xhrRequests duration in seconds
});

Summary

Summaries calculate percentiles of observed values.

Configuration

The default percentiles are: 0.01, 0.05, 0.5, 0.9, 0.95, 0.99, 0.999. But they can be overriden like this:

const client = require('prom-client');
new client.Summary({
  name: 'metric_name',
  help: 'metric_help',
  percentiles: [0.01, 0.1, 0.9, 0.99]
});

To enable the sliding window functionality for summaries you need to add maxAgeSeconds and ageBuckets to the config like this:

const client = require('prom-client');
new client.Summary({
  name: 'metric_name',
  help: 'metric_help',
  maxAgeSeconds: 600,
  ageBuckets: 5
});

The maxAgeSeconds will tell how old an bucket can be before it is reset and ageBuckets configures how many buckets we will have in our sliding window for the summary.

Usage example

const client = require('prom-client');
const summary = new client.Summary({
  name: 'metric_name',
  help: 'metric_help'
});
summary.observe(10);

Utility to observe request durations

const end = summary.startTimer();
xhrRequest(function(err, res) {
  end(); // Observes the value to xhrRequests duration in seconds
});

Uses cases

Counter

For any metric that you want to count: exceptions, status 403, requests etc.

Histogram

For the latency of the http request and MySQL queries.

Gauge

the same as Counter but this can decrease de counter.

Summary

Calculates percentiles, a percentile is a proportion of a poblation that falls in some classification.