@opentelemetry/instrumentation-express

OpenTelemetry Express Instrumentation for Node.js

This module provides automatic instrumentation for the express module, which may be loaded using the @opentelemetry/sdk-trace-node package and is included in the @opentelemetry/auto-instrumentations-node bundle.

If total installation size is not constrained, it is recommended to use the @opentelemetry/auto-instrumentations-node bundle with @opentelemetry/sdk-node for the most seamless instrumentation experience.

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.
requestHook	ExpressRequestCustomAttributeFunction (function)	(span, info) => {}	Function for adding custom attributes on Express request. Receives params: Span, ExpressRequestInfo.

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.
• defaultName: string - original name proposed by the instrumentation.

requestHook is invoked with 2 arguments:

• span: Span - the span associated with the express request.
• info: ExpressRequestInfo containing the incoming Express.js request, the current route handler creating a span and ExpressLayerType - the type of the handling layer.

NOTE: ExpressRequestInfo.request is typed as any. If you want type support make sure you have @types/express installed then you can use ExpressRequestInfo<express.Request>

Ignore a whole Express route

In order to ignore whole traces that represent a given Express route, use the ignoreIncomingRequestHook option from @opentelemetry/instrumentation-http against the route path. Ideally, this shouldn't be necessary since spans should a have low cardinality and minimize interaction between instrumentation libraries but @opentelemetry/instrumentation-express renames the root span from @opentelemetry/instrumentation-http in order to get things in order.

registerInstrumentations({
  instrumentations: [
    // Express instrumentation expects HTTP layer to be instrumented
    new HttpInstrumentation({
      ignoreIncomingRequestHook(req) {
        // Ignore spans from static assets.
        const isStaticAsset = !!req.url.match(/^\/static\/.*$/);
        return isStaticAsset;
      }
    }),
    new ExpressInstrumentation(),
  ],
});

Using requestHook

Instrumentation configuration accepts a custom "hook" function which will be called for every instrumented Express layer involved in a request. Custom attributes can be set on the span or run any custom logic per layer.

Here is a simple example that adds to the request handler span some attributes based on the Express request attributes:

import { ExpressInstrumentation, ExpressLayerType } from "@opentelemetry/instrumentation-express"

const expressInstrumentation = new ExpressInstrumentation({
  requestHook: function (
    span: Span,
    info: ExpressRequestInfo,
  ) {

    if (info.layerType === ExpressLayerType.REQUEST_HANDLER) {
      span.setAttribute(
        'http.method',
        info.request.method
      );

      span.setAttribute(
        'express.base_url',
        info.request.baseUrl
      );
    }
  }
});

Semantic Conventions

This package uses @opentelemetry/semantic-conventions version 1.22+, which implements Semantic Convention Version 1.7.0

Attributes collected:

Attribute	Short Description	Notes
http.route	The matched route (path template).	Key: SEMATTRS_HTTP_ROUTE

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.