README

OpenTelemetry Express Instrumentation for Node.js

This module provides automatic instrumentation for express.

For automatic instrumentation see the @opentelemetry/sdk-trace-node package.

Compatible with OpenTelemetry JS API and SDK 1.0+.

Installation

This instrumentation relies on HTTP calls to also be instrumented. Make sure you install and enable both, otherwise you will not see any spans being exported from the instrumentation.

npm install --save @opentelemetry/instrumentation-http @opentelemetry/instrumentation-express

Supported Versions

^4.0.0

Usage

OpenTelemetry Express Instrumentation allows the user to automatically collect trace data and export them to their backend of choice, to give observability to distributed systems.

To load the instrumentation, specify it in the Node Tracer's configuration:

const { NodeTracerProvider } = require('@opentelemetry/sdk-trace-node');
const { registerInstrumentations } = require('@opentelemetry/instrumentation');
const { HttpInstrumentation } = require('@opentelemetry/instrumentation-http');
const { ExpressInstrumentation } = require('@opentelemetry/instrumentation-express');

const provider = new NodeTracerProvider();
provider.register();

registerInstrumentations({
  instrumentations: [
    // Express instrumentation expects HTTP layer to be instrumented
    new HttpInstrumentation(),
    new ExpressInstrumentation(),
  ],
});

See examples/express for a short example.

Caveats

Because of the way express works, it's hard to correctly compute the time taken by asynchronous middlewares and request handlers. For this reason, the time you'll see reported for asynchronous middlewares and request handlers still only represent the synchronous execution time, and not any asynchronous work.

Express Instrumentation Options

Express instrumentation has few options available to choose from. You can set the following:

Options	Type	Example	Description
`ignoreLayers`	`IgnoreMatcher[]`	`[/^\/_internal\//]`	Ignore layers that by match.
`ignoreLayersType`	`ExpressLayerType[]`	`['request_handler']`	Ignore layers of specified type.
`spanNameHook`	`SpanNameHook`	`() => 'my-span-name'`	Can be used to customize span names by returning a new name from the hook.

ignoreLayers accepts an array of elements of types:

string for full match of the path,
RegExp for partial match of the path,
function in the form of (path) => boolean for custom logic.

ignoreLayersType accepts an array of following strings:

router is the name of express.Router(),
middleware,
request_handler is the name for anything that's not a router or a middleware.

spanNameHook is invoked with 2 arguments:

info: ExpressRequestInfo containing the incoming Express.js request, the current route handler creating a span and ExpressLayerType - the type of the handling layer or undefined when renaming the root HTTP instrumentation span.
defaultName: string - original name proposed by the instrumentation.

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

Apache 2.0 - See LICENSE for more information.

Usage no npm install needed!