Important: This documentation is about an older version. It's relevant only to the release noted, many of the features and functions have been updated or replaced. Please view the current version.

JavaScript API

k6/experimental

tracing

Client

Open source

Client

Client is an HTTP client constructor that attaches tracing information to its requests. Use it to include a tracing context in HTTP requests so that tracing backends (such as Grafana Tempo) can incorporate their results.

The Client class acts as a drop-in replacement for the standard http module and attaches a trace context to the requests headers, and add a trace_id to HTTP-related k6 output’s data points metadata. It currently supports the W3C Trace Context and Jaeger trace context propagation formats. For details about propagation, refer to About trace contexts.

The Client constructor accepts an Options object as its only parameter.

Example

This example demonstrates how to instantiate a tracing client and use it to instrument HTTP calls with trace context headers. It also illustrates how you can use it alongside the standard http module to perform non-instrumented HTTP calls.

import { check } from 'k6';
import tracing from 'k6/experimental/tracing';
import http from 'k6/http';

// Explicitly instantiating a tracing client allows to distringuish
// instrumented from non-instrumented HTTP calls, by keeping APIs separate.
// It also allows for finer-grained configuration control, by letting
// users changing the tracing configuration on the fly during their
// script's execution.
const instrumentedHTTP = new tracing.Client({
  propagator: 'w3c',
});

const testData = { name: 'Bert' };

export default () => {
  // Using the tracing client instance, HTTP calls will have
  // their trace context headers set.
  let res = instrumentedHTTP.request('GET', 'http://httpbin.org/get', null, {
    headers: {
      'X-Example-Header': 'instrumented/request',
    },
  });

  // The tracing client offers more flexibility over
  // the `instrumentHTTP` function, as it leaves the
  // imported standard http module untouched. Thus,
  // one can still perform non-instrumented HTTP calls
  // using it.
  res = http.post('http://httpbin.org/post', JSON.stringify(testData), {
    headers: { 'X-Example-Header': 'noninstrumented/post' },
  });

  res = instrumentedHTTP.del('http://httpbin.org/delete', null, {
    headers: { 'X-Example-Header': 'instrumented/delete' },
  });
};

HTTP module functions equivalents

The Client class exposes the same API as the standard http module. Except for the batch method, which is absent from Client. The following table lists the Client methods which have an equivalent in the standard http module:

Method	HTTP equivalent	Description
`Client.del(url, [body], [params])`	http.del	Performs an instrumented HTTP DELETE request. The method has the same prototype as the `http.del` function and should transparently act as a drop-in replacement for it.
`Client.get(url, [params])`	http.get	Performs an instrumented HTTP GET request. The method has the same prototype as the `http.get` function and should transparently act as a drop-in replacement for it.
`Client.head(url, [params])`	http.head	Performs an instrumented HTTP HEAD request. The method has the same prototype as the `http.head` function and should transparently act as a drop-in replacement for it.
`Client.options(url, [body], [params])`	http.options	Performs an instrumented HTTP OPTIONS request. The method has the same prototype as the `http.options` function and should transparently act as a drop-in replacement for it.
`Client.patch(url, [body], [params])`	http.patch	Performs an instrumented HTTP PATCH request. The method has the same prototype as the `http.patch` function and should transparently act as a drop-in replacement for it.
`Client.post(url, [body], [params])`	http.post	Performs an instrumented HTTP POST request. The method has the same prototype as the `http.post` function and should transparently act as a drop-in replacement for it.
`Client.put(url, [body], [params])`	http.put	Performs an instrumented HTTP HEAD request. The method has the same prototype as the `http.put` function and should transparently act as a drop-in replacement for it.
`Client.request(method, url, [body], [params])`	http.request	Performs an instrumented HTTP request. The method has the same prototype as the `http.request` function and should transparently act as a drop-in replacement for it.
`Client.asyncRequest(method, url, [body], [params])`	http.asyncRequest	Performs an instrumented HTTP asynchronous request. The method has the same prototype as the `http.asyncRequest` function and should transparently act as a drop-in replacement for it.