sentry-reliability-patterns

Sentry Reliability Patterns

Overview

Build Sentry integrations that never take your application down via three pillars: safe initialization with graceful degradation, a circuit breaker that stops hammering Sentry when unreachable, and an offline event queue that buffers errors during outages. Every pattern prioritizes application uptime over telemetry completeness.

Prerequisites

• @sentry/node v8+ (TypeScript) or sentry-sdk v2+ (Python)
• A valid Sentry DSN from project settings at sentry.io
• A fallback logging destination decided (console, file, or external logger)
• Understanding of your application shutdown lifecycle (signal handlers, container orchestration)

Instructions

Step 1 — Safe Initialization with Graceful Degradation

Wrap Sentry.init() in try/catch so an invalid DSN, network error, or SDK bug never crashes the app. Track initialization state with a boolean flag. Protect beforeSend callbacks with their own error boundary.

Create lib/sentry-safe.ts with initSentrySafe() and captureError(). See graceful-degradation.md for full implementation.

Key rules:

• Never let Sentry.init() crash the process — wrap in try/catch, set sentryAvailable = false on failure
• Verify client creation with Sentry.getClient() — invalid DSNs silently produce no client
• Always log errors locally as baseline before attempting Sentry capture
• Wrap user-supplied beforeSend hooks in nested try/catch — return raw event on hook failure

Step 2 — Circuit Breaker for Sentry Outages

When Sentry is unreachable, continued attempts waste resources and add latency. Track consecutive failures and trip open after a threshold. After cooldown, enter half-open state and send a single probe.

Implement SentryCircuitBreaker class with closed/open/half-open states. See circuit-breaker-pattern.md for full implementation. Expose state via health-checks.md endpoint.

Key rules:

• Default: 5 failures to trip open, 60-second cooldown before half-open probe
• In open state, skip Sentry calls entirely and log to fallback
• On half-open success, reset to closed with zero failure count
• Expose getStatus() for health check endpoints and monitoring dashboards

Step 3 — Offline Queue, Custom Transport, and Graceful Shutdown

Buffer events when network is unavailable and replay on reconnect. Use bounded file-based queue to survive restarts. Pair with signal handlers that flush via Sentry.close() before process exit.

Implement three modules:

• lib/sentry-offline-queue.ts — enqueueEvent() and drainQueue(). See network-failure-handling.md
• lib/sentry-transport.ts — Custom transport with exponential backoff retry. See timeout-handling.md
• lib/sentry-shutdown.ts — SIGTERM/SIGINT handlers calling Sentry.close(2000). See timeout-handling.md

Key rules:

• Cap offline queue at 1000 events, evict oldest when full
• Drain queue on startup and when connectivity restores
• Call Sentry.close(timeout) before process.exit() — without it, in-flight events are silently dropped
• For critical errors, use dual-write-pattern.md to send to multiple destinations via Promise.allSettled

Output

• Safe init wrapper catching SDK failures, starting app in degraded mode
• captureError() with automatic fallback to local logging
• Circuit breaker stopping sends after repeated failures, self-healing after cooldown
• Health check endpoint exposing SDK status and circuit breaker state
• File-based offline queue buffering events during outages, draining on reconnect
• Signal handlers flushing in-flight events before process exit
• Custom transport with exponential-backoff retry logic

Error Handling

Error	Cause	Solution
App crashes on Sentry.init()	Invalid DSN or SDK bug	Wrap in try/catch via initSentrySafe()
Events lost on SIGTERM	No Sentry.close() before exit	Register signal handlers with Sentry.close(2000)
Sentry outage cascades latency	Every error path hits Sentry HTTP	Circuit breaker trips after 5 failures
Events lost during network blip	SDK drops events silently	Retry transport + offline queue
Silent event loss	SDK fails without throwing	Health check probes with captureMessage + flush
Queue grows unbounded	Never drained, Sentry permanently down	Cap at 1000 events, drain on startup
beforeSend crashes pipeline	User hook throws	Nested try/catch, return raw event

See errors.md for extended troubleshooting.

Examples

See examples.md for complete TypeScript and Python integration examples including full-stack wiring of all three patterns.

Resources

• Sentry JS Configuration — beforeSend, sampleRate, init options
• Custom Transports — retry and offline transports
• Shutdown & Draining — Sentry.close() and Sentry.flush()
• Sentry Python SDK — sentry_sdk.init(), flush(), scope management
• Sentry Status Page — monitor platform outages

Next Steps

• Emit circuit breaker state changes to observability platform (Datadog, Prometheus) for outage alerting
• Set up periodic drainQueue() via setInterval (Node) or cron (Python) instead of startup-only
• Apply retry transport pattern to Python via sentry_sdk.init(transport=...) parameter
• Test failure modes in staging — simulate Sentry failures with beforeSend to verify circuit breaker behavior
• Add dual-write for P0/fatal errors to secondary destinations (CloudWatch, PagerDuty)