How to force tracing of a specific request?

[gajus]

The use case is that I want to debug specific pages, e.g.

https://contra.com/s/gUvPcLrL-open-source-consultation

This page is loading really slowly at the moment, and I would like to get a trace that explains it.

We can inject data into client and pass it to the server.

e.g. This is what I was thinking of client-side

const createSentry = ({
  dsn,
  environment,
  release,
}: {
  dsn?: string;
  environment?: string;
  release?: string;
}) => {
  log.debug('sentry initialized');

  let tracesSampleRate = 0.05;

  // Allow overriding traces sample rate via sessionStorage.
  // Example: sessionStorage.setItem('CONTRA_TRACES_SAMPLE_RATE', '1');
  const tracesSampleRateSessionOverride = sessionStorage.getItem(
    'CONTRA_TRACES_SAMPLE_RATE',
  );

  if (tracesSampleRateSessionOverride) {
    tracesSampleRate = Number.parseFloat(tracesSampleRateSessionOverride);

    log.debug(
      'traces sample rate overridden via sessionStorage (%s)',
      tracesSampleRate,
    );
  }

  return init({
    dsn,
    environment,
    integrations: [new BrowserTracing()],
    normalizeDepth: 5,
    profilesSampleRate: 0.05,
    release,
    tracePropagationTargets: [/^\/api\//u],
    tracesSampleRate,
  });
};

But how to tell backend to know that it has to trace requests originating from this session?

[lforst]

It depends on what language/SDK you're using on the backend. Usually the SDKs will automatically pick up incoming traces.

[gajus]

My original question stands... how do I tell Sentry to trace the specific request? Let's say from within Node.js

[lforst]

What server framework are you using?

[gajus]

I need to know how to do it in plain JS.

[AbhiPrasad]

You can use the tracesSampler option to force a sampling decision based on values in transaction context https://docs.sentry.io/platforms/javascript/configuration/options/#traces-sampler

[gajus]

Thanks @AbhiPrasad

[lforst]

@AbhiPrasad but shouldn't the downstream trace inherit the previous trace decision? I honestly thought that this issue was gonna be about distributed tracing not working (being set up).

[gajus]

It turned to be an issue indeed!

For now, I ended up disabling sampling just while we are still figuring out how everything works.

Still cannot get the first leg to work.

#9870 (reply in thread)

You can see this in progress here:

https://contra.com/gajus

Now the traces do not appear at all.

[lforst]

I recommend reading https://docs.sentry.io/platforms/node/usage/distributed-tracing/custom-instrumentation/ to understand how to connect services.