@opentelemetry/instrumentation-fetch

What is @opentelemetry/instrumentation-fetch?

@opentelemetry/instrumentation-fetch is an npm package that provides automatic instrumentation for the Fetch API, allowing developers to collect telemetry data such as traces and metrics for HTTP requests made using the Fetch API. This is useful for monitoring and debugging web applications.

What are @opentelemetry/instrumentation-fetch's main functionalities?

Automatic Tracing

This feature allows you to automatically trace HTTP requests made using the Fetch API. The code sample demonstrates how to set up the FetchInstrumentation and enable it to start collecting trace data.

const { FetchInstrumentation } = require('@opentelemetry/instrumentation-fetch');
const { NodeTracerProvider } = require('@opentelemetry/node');
const { SimpleSpanProcessor } = require('@opentelemetry/tracing');
const { ConsoleSpanExporter } = require('@opentelemetry/tracing');

const provider = new NodeTracerProvider();
provider.addSpanProcessor(new SimpleSpanProcessor(new ConsoleSpanExporter()));
provider.register();

const fetchInstrumentation = new FetchInstrumentation();
fetchInstrumentation.enable();

fetch('https://jsonplaceholder.typicode.com/todos/1')
  .then(response => response.json())
  .then(json => console.log(json));

Custom Attributes

This feature allows you to add custom attributes to the spans created for Fetch API requests. The code sample shows how to set a custom attribute on each span.

const { FetchInstrumentation } = require('@opentelemetry/instrumentation-fetch');
const { NodeTracerProvider } = require('@opentelemetry/node');
const { SimpleSpanProcessor } = require('@opentelemetry/tracing');
const { ConsoleSpanExporter } = require('@opentelemetry/tracing');

const provider = new NodeTracerProvider();
provider.addSpanProcessor(new SimpleSpanProcessor(new ConsoleSpanExporter()));
provider.register();

const fetchInstrumentation = new FetchInstrumentation({
  applyCustomAttributesOnSpan: (span, request, response) => {
    span.setAttribute('custom-attribute', 'custom-value');
  }
});
fetchInstrumentation.enable();

fetch('https://jsonplaceholder.typicode.com/todos/1')
  .then(response => response.json())
  .then(json => console.log(json));

Error Handling

This feature allows you to handle errors in Fetch API requests and optionally ignore certain URLs or HTTP methods from being instrumented. The code sample demonstrates how to set up error handling and ignore specific URLs and methods.

const { FetchInstrumentation } = require('@opentelemetry/instrumentation-fetch');
const { NodeTracerProvider } = require('@opentelemetry/node');
const { SimpleSpanProcessor } = require('@opentelemetry/tracing');
const { ConsoleSpanExporter } = require('@opentelemetry/tracing');

const provider = new NodeTracerProvider();
provider.addSpanProcessor(new SimpleSpanProcessor(new ConsoleSpanExporter()));
provider.register();

const fetchInstrumentation = new FetchInstrumentation({
  ignoreUrls: [/example\.com/],
  ignoreMethods: ['POST']
});
fetchInstrumentation.enable();

fetch('https://jsonplaceholder.typicode.com/todos/1')
  .then(response => response.json())
  .then(json => console.log(json))
  .catch(error => console.error('Fetch error:', error));

Other packages similar to @opentelemetry/instrumentation-fetch

axios

Axios is a popular HTTP client for making requests from both the browser and Node.js. While it does not provide automatic instrumentation out of the box, it can be integrated with OpenTelemetry using custom instrumentation. Compared to @opentelemetry/instrumentation-fetch, Axios offers more features for making HTTP requests but requires additional setup for telemetry.

got

Got is another HTTP client for Node.js that is known for its simplicity and performance. Similar to Axios, it does not provide automatic instrumentation but can be integrated with OpenTelemetry through custom instrumentation. Got is often preferred for its lightweight and efficient design compared to @opentelemetry/instrumentation-fetch.

node-fetch

Node-fetch is a lightweight module that brings the Fetch API to Node.js. It is similar to the Fetch API in the browser and can be instrumented using @opentelemetry/instrumentation-fetch. However, node-fetch itself does not provide built-in telemetry capabilities, making it less feature-rich in terms of monitoring compared to @opentelemetry/instrumentation-fetch.

README

OpenTelemetry Fetch Instrumentation for web

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

This module provides auto instrumentation for web using fetch. (Note: This instrumentation does not instrument Node.js' fetch. See @opentelemetry/instrumentation-undici for that.)

Installation

npm install --save @opentelemetry/instrumentation-fetch

Usage

import {
  ConsoleSpanExporter,
  SimpleSpanProcessor,
  WebTracerProvider,
} from '@opentelemetry/sdk-trace-web';
import { FetchInstrumentation } from '@opentelemetry/instrumentation-fetch';
import { ZoneContextManager } from '@opentelemetry/context-zone';
import { registerInstrumentations } from '@opentelemetry/instrumentation';

const provider = new WebTracerProvider({
  spanProcessors: [new SimpleSpanProcessor(new ConsoleSpanExporter())]
});

provider.register({
  contextManager: new ZoneContextManager(),
});

registerInstrumentations({
  instrumentations: [new FetchInstrumentation()],
});

// or plugin can be also initialised separately and then set the tracer provider or meter provider
const fetchInstrumentation = new FetchInstrumentation();
const provider = new WebTracerProvider({
  spanProcessors: [new SimpleSpanProcessor(new ConsoleSpanExporter())]
});
provider.register({
  contextManager: new ZoneContextManager(),
});
fetchInstrumentation.setTracerProvider(provider);

// and some test

fetch('http://localhost:8090/fetch.js');

Example Screenshots

See examples/tracer-web/fetch for a short example.

Fetch Instrumentation options

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

Options	Type	Description
applyCustomAttributesOnSpan	FetchCustomAttributeFunction	Function for adding custom attributes
requestHook	FetchRequestHookFunction	Function for adding custom attributes or headers before the request is handled
ignoreNetworkEvents	boolean	Disable network events being added as span events (network events are added by default)
measureRequestSize	boolean	Measure outgoing request length (outgoing request length is not measured by default)
semconvStabilityOptIn	string	A comma-separated string of tokens as described for OTEL_SEMCONV_STABILITY_OPT_IN in the HTTP semantic convention stability migration guide. See the "Semantic Conventions" section below.

Semantic Conventions

Up to and including v0.200.0, instrumentation-fetch generates telemetry using Semantic Conventions v1.7.0.

HTTP semantic conventions (semconv) were stabilized in semconv v1.23.0, and a migration process was defined. instrumentation-fetch versions 0.201.0 and later include support for migrating to stable HTTP semantic conventions, as described below. The intent is to provide an approximate 6 month time window for users of this instrumentation to migrate to the new HTTP semconv, after which a new minor version will change to use the new semconv by default and drop support for the old semconv. See the HTTP semconv migration plan for OpenTelemetry JS instrumentations.

To select which semconv version(s) is emitted from this instrumentation, use the semconvStabilityOptIn configuration option. This option works as described for OTEL_SEMCONV_STABILITY_OPT_IN:

• http: emit the new (stable) v1.23.0 semantics
• http/dup: emit both the old v1.7.0 and the new (stable) v1.23.0 semantics
• By default, if semconvStabilityOptIn includes neither of the above tokens, the old v1.7.0 semconv is used.

Span name: With the old v1.7.0 semconv the span name is HTTP {method} (for example 'HTTP GET'). Using the stable semconv v1.23 for HTTP span names, the span name is {method} (for example 'GET'). If both semconv versions are being emitted, the old name wins. (This instrumentation does not currently support adding an {http.route} to the span name.)

Span status: When the stable semconv is selected, the span status is set to ERROR when the response status code is >=400. When just the old semconv is select, the span status is not set.

Span attributes:

v1.7.0 semconv	v1.23.0 semconv	Notes
http.method	http.request.method	HTTP request method. With v1.23.0 semconv http.request.method_original may also be included.
http.url	url.full	Full HTTP request URL
http.host	server.address and server.port	The hostname and port of the request URL
http.status_code	http.response.status_code	HTTP response status code
http.request_content_length_uncompressed	http.request.body.size	This is only added if measureRequestSize is true.
http.response_content_length_uncompressed	(not included)	Stable HTTP semconv would use http.response.body.size, but this is an Opt-In attribute, so would require adding a configuration option to this instrumentation to enable.
http.response_content_length	(not included)	Stable HTTP semconv would use http.response.header.<key>, but this is an Opt-In attribute, so would require adding a configuration option to this instrumentation to enable.
(no equivalent)	error.type	The response status (as a string), if the response status was >=400.
http.user_agent	(not included)	Stable HTTP semconv would use user_agent.original, but this is an Opt-In attribute, so would require adding a configuration option to this instrumentation to enable.
http.scheme	(not included)	Stable HTTP semconv would use url.scheme, but this is an Opt-In attribute, so would require adding a configuration option to this instrumentation to enable.
http.status_text	(not included)	This is no longer a documented semantic conventions attribute.
component	(no replacement)	component was an ancient Span "tag" that was never formalized.

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.