@nifty-lil-tricks/monitoring

Note: This is an experimental package under active development. New releases may include breaking changes.

A selection of useful utilities (or nifty li'l tricks!) for all things monitoring and OpenTelemetry.

Table of contents

• Installation
• Features
• API
• Examples
• Support
• Useful links
• License
• Contributions

Installation

Note: this package works with TypeScript v5 or later

npm install @nifty-lil-tricks/monitoring

Experimental stage 2 decorators

If you are using experimental stage 2 decorators, you will need to set the following in your tsconfig.json:

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}

Stage 3 decorators

No setup is required.

Features

The following features are supported

• Monitoring decorator that wraps all methods of a class in an OpenTelemetry Span automatically tracing every method on the class.

Monitoring Decorator

• @nifty-lil-tricks/monitoring
  • Table of contents
  • Installation
    • Experimental stage 2 decorators
    • Stage 3 decorators
  • Features
    • Monitoring Decorator
      • Monitoring Decorator Overview
        • Exported span for method that passes
        • Exported span for method that throws
      • Pre-requisites
      • Wrap all methods of a class in a span
      • Filter allowed methods to monitor
        • Filtering monitored methods by list of strings
        • Filtering monitored methods by regex
        • Filtering monitored methods by function
      • Override the default Span kind
      • Override the inferred class name
      • Override the default tracer name
      • Caveats
  • API
  • Examples
    • Basic example
    • Nestjs example
  • Support
  • Useful links
  • License
  • Contributions

Monitoring Decorator Overview

This decorator wraps all methods of a class in an OpenTelemetry Span. If a parent span cannot be retrieved from the context of the method call, it will not be monitored.

The decorator will not affect any of the underlying functionality and it will also handle any legitimate errors thrown from the underlying method as appropriate.

Exported span for method that passes

A method of name hello on class Service that returns without error will export the following span details by default:

{
  "id": "b98126c289c5c9dc",
  "name": "Service.hello",
  "traceId": "a7b41739082880c506d62152de2e13a1",
  "parentId": "f64d1571cd4a88dd",
  "kind": 0,
  "attributes": {
    "monitoring.method": "hello",
    "monitoring.class": "Service"
  },
  "status": { "code": 1 },
  "timestamp": 1684136794317000,
  "duration": 2010408,
  "events": [],
  "links": []
}

Exported span for method that throws

A method of name hello on class Service that throws an error will export the following span details by default:

{
  "id": "7c5f84a384af9a63",
  "name": "Service.hello",
  "traceId": "931ba33b4ab375ade4f26c7ac93df4ce",
  "parentId": "0182507d0f5f0a85",
  "kind": 0,
  "attributes": {
    "monitoring.method": "hello",
    "monitoring.class": "Service"
  },
  "status": { "code": 2, "message": "Error: something bad happened" },
  "timestamp": 1684136986170000,
  "duration": 502605,
  "events": [],
  "links": []
}

Pre-requisites

Ensure OpenTelemetry tracing is set-up by ensuring:

• The provider is registered
• The monitored method is wrapped in the context of a parent span
• A global context manager is set up

See example set up for a quick guide to getting the above setup.

Wrap all methods of a class in a span

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor()
class Service {
  async hello(): Promise<void> {
    // Do work
    await promisify(setTimeout)(500);

    // Do nested work
    await this.nested();
  }

  async nested(): Promise<void> {
    // Do work
    await promisify(setTimeout)(1000);
  }
}

Filter allowed methods to monitor

By default, the monitor decorator monitors all non-private methods. One can provide an allowedMethods option to filter the methods that are monitored. This filter can be provided in several types:

• string[]
• RegExp
• (methodName: string) => boolean

Filtering monitored methods by list of strings

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor({ allowedMethods: ["allowed1", "allowed2"] })
class Service {
  // Not monitored
  notAllowed(): void {}

  // Monitored
  allowed1(): void {}

  // Monitored
  allowed2(): void {}
}

Filtering monitored methods by regex

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor({ allowedMethods: /^allowed.+/ })
class Service {
  // Not monitored
  notAllowed(): void {}

  // Monitored
  allowed1(): void {}

  // Monitored
  allowed2(): void {}
}

Filtering monitored methods by function

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor({ allowedMethods: (method) => method.startsWith("allowed") })
class Service {
  // Not monitored
  notAllowed(): void {}

  // Monitored
  allowed1(): void {}

  // Monitored
  allowed2(): void {}
}

Override the default Span kind

By default, the monitor decorator sets the Span Kind to be INTERNAL. This option allows one to override this.

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor({ spanKind: SpanKind.SERVER })
class Service {
  async hello(): Promise<void> {
    // Do work
    await promisify(setTimeout)(500);
  }
}

Override the inferred class name

By default, the monitor decorator infers the class name from the class. This option allows one to override this behaviour. A use-case for this would be when one has multiple classes of the same name defined.

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor({ className: "OtherService" })
class Service {
  async hello(): Promise<void> {
    // Do work
    await promisify(setTimeout)(500);
  }
}

Override the default tracer name

By default, the monitor decorator uses the default tracer to record spans. This option allows one to override this behaviour.

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor({ tracerName: "some-other-tracer" })
class Service {
  async hello(): Promise<void> {
    // Do work
    await promisify(setTimeout)(500);
  }
}

Caveats

Private methods as defined here are not monitoring by this decorator.

import { Monitor } from "@nifty-lil-tricks/monitoring";
import { promisify } from "node:util";

@Monitor({ tracerName: "some-other-tracer" })
class Service {
  // Monitored
  async hello(): Promise<void> {
    // Not monitored
    await this.#privateMethod(())
  }

  async #privateMethod(): Promise<void> {
    // Do work
    await promisify(setTimeout)(500);
  }
}

API

The API docs can be found here

Examples

Examples can be found here.

Basic example

To run the examples/basic.ts example, run the following:

• Ensure Docker is running
• Start the Jaeger collector: npm run start:collector
• Run the example: npm run example:basic
• Navigate to the Jaeger UI: http://localhost:16686

Nestjs example

To run the examples/basic.ts example, run the following:

• Ensure Docker is running
• Start the Jaeger collector: npm run start:collector
• Run the example: npm run example:nestjs
• Make a request to the app: curl http://localhost:3000/
• Navigate to the Jaeger UI: http://localhost:16686

Support

Platform Version	Supported	Notes
Node.JS v18	✅	TypeScript v5+ for typings
Node.JS v20	✅	TypeScript v5+ for typings
Deno v1	❌	Will be supported when OpenTelemetry is supported in Deno
Web Browsers	❌	Coming soon

Useful links

• For more information on OpenTelemetry, visit: https://opentelemetry.io/
• For more about OpenTelemetry JavaScript: https://github.com/open-telemetry/opentelemetry-js
• For help or feedback on this project, join us in GitHub Discussions

License

Nifty li'l tricks packages are 100% free and open-source, under the MIT license.

This package is Treeware. If you use it in production, then we ask that you buy the world a tree to thank us for our work. By contributing to the Treeware forest you’ll be creating employment for local families and restoring wildlife habitats.

Contributions

Contributions, issues and feature requests are very welcome. If you are using this package and fixed a bug for yourself, please consider submitting a PR!