socket.io-prometheus-tracker

Track metrics for a Socket.IO server for use in Prometheus.

Note that by its nature this library relies on monkey-patching the socket.io server instance to hook into functions like socket.emit. Bear this in mind if you're applying any monkey-patches of your own, and please read the source code to ensure compatibility.

Library aims:

• Cover all Socket.IO events in the default namespace, sent or received.
• Just track metrics. You can do what you want with them - serve via express, periodically write to a file, whatever.

Useful links:

• Documentation
• Code Coverage Report
• Unit Test Report

Contents

1. Intro
2. Configuration
3. Metrics
4. Examples
   • Basic Use
   • Configuring Instances
   • Express Application
5. Contributing
   • Useful Snippets
6. Feedback and Support

Configuration

When instantiating SocketIOPrometheusTracker, you can optionally pass a configuration object. Available parameters are listed below:

Option	Default Value	Summary
collectDefaultMetrics	false	Should the library also collect metrics recommended by Prometheus. Note that this will increase the number of exposed metrics beyond those listed in Metrics. See: https://github.com/siimon/prom-client#default-metrics for more details.
prometheusClient	undefined	An instance of prom-client the library uses to determine the registry for storing metrics. If not provided, the default registry will be used.
trackSocketId	false	Should a label be included for additionally tracking the socket id where appropriate. This may be useful for debugging, but is not recommended for use in production. This will lead to the size of the registry growing indefinitely over time. Events affected by this value are noted in Metrics.

Metrics

Name	Labels	Summary
socketio_bytes_received_total	['event', 'socketid*']	Total number of bytes received by the server.
socketio_bytes_sent_total	['event']	Total number of bytes sent by the server.
socketio_connects_current	[]	Current number of clients connected to the server.
socketio_connects_length	['socketid*']	The length in seconds of connections to the server.
socketio_connects_total	[]	Total number of connections that have been made to the server.
socketio_disconnects_total	[]	Total number of disconnections from the server.
socketio_events_received_total	['event', 'socketid*']	Total number of events received by the server.
socketio_events_sent_total	['event']	Total number of events sent by the server.

_{* Field socketid will only be included if configuration option trackSocketId is set to true.}

Things to be aware of

Namespaces

Events emitted outbound via the Server instance should be tracked successfully regardless of the namespace used. Events emitted outbound via a Socket instance are currently only tracked in the default namespace.

The library exports all functions used, so feel free to setup hooks against any custom namespaces you want on top of the default behavior.

Examples

Basic Use

The tracker can be instantiated by passing an instance of a Socket.IO server.

const ioPrometheus = new SocketIOPrometheusTracker(io);

Metrics can then be accessed using: ioPrometheus.register.metrics();

Configuring Instances

const ioPrometheus = new SocketIOPrometheusTracker(io, {
  collectDefaultMetrics: true,
  trackSocketId: true,
});

Express Application

An example project using the library can be found in ./examples/express.

Contributing

While contributions are appreciated, they may be rejected if not in line with the intended project direction. It's recommended to check before undertaking a major piece of work and/or refactoring.

Contributions should be based off the develop branch, and any pull requests made into develop.

Pull requests should include a corresponding entry in CHANGELOG.md.

Useful Snippets

// Install dependencies
npm ci

// Run tests
npm run lint
npm run test

// Build the library
npm run build

Feedback and Support

For suggestions, issues, and/or support raise a GitHub issue!