Sentry

Error tracking and performance monitoring for both frontend and backend. Captures unhandled exceptions, performance traces, and session replays to aid debugging in deployed environments.

Architecture

Component	Path	Purpose
Backend setup	top of backend/src/index.ts	@sentry/bun init before any other imports, beforeSend scrubbing
Backend capture	backend/src/middleware/errorHandler.ts	Sentry.captureException with user context
Frontend setup	frontend/src/main.tsx	@sentry/react init, tracing, session replay, error boundary

There is no separate lib/sentry.ts — backend init lives directly at the top of index.ts so it runs before everything else.

Configuration

Variable	Purpose
SENTRY_DSN_BACKEND	Backend error reporting endpoint
VITE_SENTRY_DSN_FRONTEND	Frontend DSN (build-time, public)

Secrets live in Infisical (EU) and sync natively to Fly.io. See Deployment Pipeline.

Environment Awareness

Sentry is enabled in all cloud deployments — APP_ENV in development, preview, staging, production (rationale: fail fast, catch errors early). Excluded: local (docker-compose) and test (CI). Events are tagged with:

• environment: the APP_ENV value
• release: COMMIT_SHA or FLY_IMAGE_REF from CI/CD

Performance sampling: tracesSampleRate is 0.1 in production, 1.0 everywhere else.

Backend Integration

The error handler middleware (backend/src/middleware/errorHandler.ts) is the last middleware in the Backend Middleware pipeline. It:

1. Catches all unhandled exceptions from routes and services
2. Attaches request context (URL, method, user ID) and captures to Sentry (cloud envs with DSN only)
3. Returns a structured JSON error response to the client

See Error Handling Pattern for the error response format.

Sensitive Data Scrubbing

The backend beforeSend hook (in index.ts) strips sensitive fields before events leave the process — case-insensitive matching on patterns including password, passwordHash, token, accessToken, refreshToken, resetToken, secret, apiKey, privateKey, credential, authorization, plus auth/cookie headers. The frontend beforeSend scrubs sensitive breadcrumb data (form inputs such as passwords).

Frontend Integration

frontend/src/main.tsx (@sentry/react) includes:

Feature	Detail
Error boundary	Sentry.ErrorBoundary wrapping the app with ErrorFallback
Session replay	replayIntegration with maskAllText, blockAllMedia, maskAllInputs
Performance tracing	browserTracingIntegration
Breadcrumb scrubbing	beforeSend removes password fields from breadcrumb data

Related

• Error Handling Pattern — Structured error responses
• Backend Middleware — Error handler middleware position
• External Integrations — All third-party integrations
• Frontend Architecture — Frontend Sentry setup
• CI-CD Workflows — Release tagging on deploy
• Security Scanning — Complementary security monitoring