Tracing without Performance

[stephanie-anderson]

Problem Statement

It should be possible that tracing information is propagated from/to incoming/outgoing HTTP requests even if performance is disabled and thus no transactions/spans are available.

Solution Brainstorm

Requirements:

1. All error, transaction and check-in events sent to Sentry always contain a Dynamic Sampling Context (trace) envelope header item.
2. All error, transaction and check-in events sent to Sentry always contain a trace context.
3. All outgoing HTTP requests always contain a sentry-trace and baggage header if the destination is allow-listed in [tracePropagationTargets](https://develop.sentry.dev/sdk/performance/#tracepropagationtargets).

### Part 1: Standardize `tracePropagationTargets`
- [ ] https://github.com/getsentry/sentry-javascript/pull/8395
- [ ] https://github.com/getsentry/sentry-javascript/pull/8399
- [ ] https://github.com/getsentry/sentry-docs/pull/7267
- [x] Deprecate `BrowserTracing` `tracePropogationTargets` in favour of top level option

### Part 2: Setting up PropagationContext
- [ ] https://github.com/getsentry/sentry-javascript/pull/8421
- [ ] https://github.com/getsentry/sentry-javascript/pull/8422
- [ ] https://github.com/getsentry/sentry-javascript/pull/8426
- [ ] https://github.com/getsentry/sentry-javascript/pull/8427
- [ ] https://github.com/getsentry/sentry-javascript/pull/8428
- [ ] https://github.com/getsentry/sentry-javascript/pull/8430
- [ ] https://github.com/getsentry/sentry-javascript/pull/8429
- [ ] https://github.com/getsentry/sentry-javascript/pull/8425
- [x] ~Make sure we support `sentry-trace` when it is an array~ [WON'T DO]

### Part 3: Tracing without Performance
- [ ] https://github.com/getsentry/sentry-javascript/pull/8434
- [ ] https://github.com/getsentry/sentry-javascript/pull/8449
- [ ] https://github.com/getsentry/sentry-javascript/pull/8450
- [ ] https://github.com/getsentry/sentry-javascript/pull/8458
- [ ] https://github.com/getsentry/sentry-javascript/pull/8503
- [x] Add DSC trace header to all outgoing envelopes
- [x] ~[OPTIONAL] Update transaction creation to use `PropagationContext`~ [WON'T DO]
- [ ] https://github.com/getsentry/sentry-javascript/issues/8520

### Part 5: Final touches
- [x] Run e2e test to show it works (replay, crons, errors) - head SDK + tail SDK
- [ ] https://github.com/getsentry/sentry-docs/pull/7421
- [ ] https://github.com/getsentry/sentry-javascript/pull/8517
- [ ] Write down key changes needed for React Native/Electron adopting Tracing without Performance

[AbhiPrasad]

We might want to explore if it's worth it to create a separate integration for browser JS that enables distributed tracing, but not take the bundle size hit of all of performance monitoring.

[danielkhan]

We might want to explore if it's worth it to create a separate integration for browser JS that enables distributed tracing, but not take the bundle size hit of all of performance monitoring.

Each dedicated package increases complexity for us but also for our users.
Additionally, it makes it harder to transition to performance as they have to change the SDK.

If the difference isn't really game-changing significant, I would not do that right now.

[AbhiPrasad]

Each dedicated package increases complexity for us but also for our users.

This wouldn't be a dedicated package, but instead just a different integration exported from Sentry. Swapping them would be as easy as removing one integration and using another.

import * as Sentry from '@sentry/browser';

Sentry.init({
  integrations: [
    // Tracing + Performance Monitoring
    // Sentry.BrowserTracing(),
    //
    // Just Tracing (name tbd, hardest problem in computer science and all of that)
    // Sentry.PlainTracing
  ],
});