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Sentry

Sentry (sentry.io) is a SaaS error-tracking and application-performance-monitoring platform widely used for frontend and backend application error capture. For frontend applications it integrates as a browser SDK that collects uncaught exceptions, Promise rejections, performance-timing data, and console warnings, enriches them with breadcrumbs / source-maps / release tags, and forwards them to a dashboard + alerting backend.

This wiki's scope for Sentry is narrow: how production React applications use Sentry to observe hydration-mismatch errors and how to keep Sentry's signal actionable in that context.

Use at Zalando Fashion Store (2023)

Zalando's Rendering Engine integrates Sentry as the destination for React 18's onRecoverableError callbacks. Post-React-18 migration, the team found that a single hydration mismatch produced many Sentry events (see patterns/first-error-only-hydration-error-reporting) because the mismatch broke fiber-vs-DOM list alignment and every subsequent node logged a consequence error.

Mitigation: "we modified our error tracking code to only send the first hydration error log to Sentry." (Source: sources/2023-07-10-zalando-rendering-engine-tales-road-to-concurrent-react.)

Observability-level insight from this: error-tracker event volume is itself a signal that can mislead. A cascade of onRecoverableError calls looks like dozens of bugs but is really one bug with post-error list-alignment drift. Dedup at the SDK integration layer turns the event stream from noise back into signal.

Relevant primitives (for this wiki)

• Sentry.captureException(error, context) — the standard call for reporting an error with enrichment.
• onRecoverableError integration — React 18's hydrateRoot callback, which production apps wire up to Sentry for hydration-mismatch observability.
• componentStack — included in errorInfo; source-mapped in Sentry's UI for readable React fiber traces.
• Tags / grouping / fingerprinting — used to dedupe cascades and surface outliers.

Stub

This page only covers Sentry as it appears in currently-ingested sources (one instance: Zalando's React 18 integration). Broader Sentry architecture (their ingestion pipeline, storage, query engine, performance-monitoring stack, replay feature, cron-monitoring, session-replay) is out of scope until a Sentry engineering post is ingested.

Seen in

• sources/2023-07-10-zalando-rendering-engine-tales-road-to-concurrent-react — Zalando Fashion Store's production Sentry integration for React 18 hydration error reporting, with the first-error-only deduplication modification called out as a production reliability fix.

Related

• systems/react — the source of onRecoverableError callbacks the Sentry SDK integrates with.
• concepts/react-hydration — the mechanism whose errors flow to Sentry.
• concepts/hydration-mismatch — the error class.
• patterns/first-error-only-hydration-error-reporting — the dedup pattern Zalando applies at the SDK boundary.