Custom Instrumentation

On this page you will learn how to manually propagate trace information into and out of your JavaScript application.

Distributed tracing will be set up automatically if:

• You've Set Up Performance in Sentry.
• You're using one of the SDKs that include distributed tracing out of the box:
  • @sentry/nextjs
  • @sentry/sveltekit
  • @sentry/remix
  • @sentry/astro

If you are using a different package, and have not enabled performance monitoring, you can manually set up your application for distributed tracing to work.

Enabling Distributed Tracing

To enable distributed tracing for your frontend, add the BrowserTracing integration to your Sentry.init() options as described in the Automatic Instrumentation docs.

If you want to use distributed tracing but not performance monitoring, set the tracesSampleRate option to 0.

Sentry.init({
  dsn: 'https://examplePublicKey@o0.ingest.sentry.io/0',
  integrations: [Sentry.browserTracingIntegration()],

  // If this is 0, performance monitoring is disabled
  // but distributed tracing is not
  tracesSampleRate: 0,
});

Enabling Distributed Tracing without BrowserTracing

If you don't want to use the BrowserTracing integration, you can manually extract and inject tracing data in your application to connect multiple systems. For this, you must:

• Extract and store incoming tracing information from HTML <meta> tags when loading the page.
• Inject tracing information to any outgoing requests.

To learn more about distributed tracing, see our Distributed Tracing docs.

Extract Tracing Information From HTML meta Tags

If you have a server that renders your application's HTML (SSR) and is also running a Sentry SDK, you can connect your backend to your backend via tracing.

To do this, have your server render HTML <meta> tags with the Sentry trace information. In your frontend, extract that tracing information when the page is loading and use it to create new transactions connected to that incoming backend trace.

Some Sentry backend SDKs provide a built-in way to inject these <meta> tags into rendered HTML. For example:

• Python
• Ruby
• PHP

Then, on pageload you can do the following:

// Read meta tag values
const sentryTrace = document.querySelector('meta[name=sentry-trace]')?.content;
const baggage = document.querySelector('meta[name=baggage]')?.content;

Sentry.continueTrace({sentryTrace, baggage}, transactionContext => {
  Sentry.startSpan(
    {
      ...transactionContext,
      name: `Pageload: ${window.location.pathname}`,
      op: 'pageload',
    },
    () => {
      // do something
    }
  );
});

In this example, we create a new transaction that is attached to the trace specified in the sentry-trace and baggage HTML <meta> tags.

If you want to use distributed tracing but not performance monitoring, set the tracesSampleRate option to 0.

Sentry.init({
  dsn: 'https://examplePublicKey@o0.ingest.sentry.io/0',

  // If this is 0, performance monitoring is disabled
  // but distributed tracing is not
  tracesSampleRate: 0,
});

Manually Extracting and Injecting Distributed Tracing Information

You can also manually extract and inject tracing data into your application. For this, you must:

• Extract and store incoming tracing information from incoming request headers or similar.
• Inject tracing information to any outgoing requests.

To learn more about distributed tracing, see our Distributed Tracing docs.

Extracting Incoming Tracing Information

You must extract and store incoming tracing information in memory for later use. Sentry provides the continueTrace() function to help you with this. Incoming tracing information can come from different places:

• In a web environment, it's sent with HTTP headers, for example, by another Sentry SDK used in your frontend project.
• In a job queue, it can be retrieved from meta or header variables.
• You also can pick up tracing information from environment variables.

Here's an example of how to extract and store incoming tracing information using continueTrace():

const http = require('http');

http.createServer((request, response) => {
  const sentryTraceHeaders = request.headers['sentry-trace'];
  const sentryTrace = Array.isArray(sentryTraceHeaders)
    ? sentryTraceHeaders.join(',')
    : sentryTraceHeaders;
  const baggage = request.headers['baggage'];

  Sentry.continueTrace({sentryTrace, baggage}, transactionContext => {
    Sentry.startSpan(
      {
        ...transactionContext,
        name: 'my request',
        op: 'http.server',
      },
      () => {
        // Your API code...
      }
    );
  });
});

In this example, we create a new transaction that is attached to the trace specified in the sentry-trace and baggage headers.

Inject Tracing Information to Outgoing Requests

For distributed tracing to work, the two headers that you extracted and stored in the active root span, sentry-trace and baggage, must be added to outgoing HTTP requests.

Here's an example of how to collect and inject this tracing information to outgoing requests:

const activeSpan = Sentry.getActiveSpan();
const rootSpan = activeSpan ? Sentry.getRootSpan(activeSpan) : undefined;

// Create `sentry-trace` header
const sentryTraceHeader = rootSpan ? Sentry.spanToTraceHeader(rootSpan) : undefined;

// Create `baggage` header
const sentryBaggageHeader = rootSpan ? Sentry.spanToBaggageHeader(rootSpan) : undefined;

// Make outgoing request
fetch('https://example.com', {
  method: 'GET',
  headers: {
    baggage: sentryBaggageHeader,
    'sentry-trace': sentryTraceHeader,
  },
}).then(response => {
  // ...
});

In this example, tracing information is propagated to the project running at https://example.com. If this project uses a Sentry SDK, it will extract and save the tracing information for later use.

The two services are now connected with your custom distributed tracing implementation.

Verification

If you make outgoing requests from your project to other services, check if the headers sentry-trace and baggage are present in the request. If so, distributed tracing is working.