@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

``shell
npm install @nifty-lil-tricks/monitoring
`

$3

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

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

$3

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.

$3

- @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:

`json
{
"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:

`json
{
"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

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

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

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

async nested(): Promise {
// 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

`typescript
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

`typescript
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

`typescript
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.

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

@Monitor({ spanKind: SpanKind.SERVER })
class Service {
async hello(): Promise {
// 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.

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

@Monitor({ className: "OtherService" })
class Service {
async hello(): Promise {
// 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.

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

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

#### Caveats

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

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

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

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

API

The API docs can be found
here

Examples

Examples can be found
here.

$3

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

!Example exported trace

$3

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

!Example exported trace

Support

| Platform Version | Supported | Notes |
| ---------------- | ------------------ | --------------------------------------------------------- |
| Node.JS v18 | :white_check_mark: | TypeScript v5+ for typings |
| Node.JS v20 | :white_check_mark: | TypeScript v5+ for typings |
| Deno v1` | :x: | Will be supported when OpenTelemetry is supported in Deno |
| Web Browsers | :x: | 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!