Performance Monitoring for Web Applications

Performance monitoring answers two questions: is the application working? Is it fast? Without monitoring, you discover problems when users complain or revenue drops.

Application Performance Monitoring (APM): tools like Datadog, New Relic, and Sentry track server-side request processing, database queries, external API calls, and error rates.

Real User Monitoring (RUM): captures actual user performance data from browsers worldwide. Unlike synthetic tests that measure ideal conditions, RUM shows real-world experience across devices and networks.

Core Web Vitals monitoring: track LCP, INP, and CLS continuously. Google's CrUX data (via PageSpeed Insights) shows field metrics. web-vitals library captures metrics in your analytics.

Error tracking: Sentry, Bugsnag, or LogRocket capture JavaScript errors with stack traces, user context, and replay capabilities. Group and prioritize errors by impact and frequency.

Uptime monitoring: services like Better Uptime, Pingdom, and UptimeRobot check availability every 30-60 seconds. Instant alerts when downtime is detected. Track uptime SLA (target 99.9%+).

Log aggregation: centralize logs from all application components using Logtail, Datadog Logs, or CloudWatch. Structured logging (JSON format) enables searching and alerting on specific events.

Alerting strategy: alert on symptoms (high error rate, slow response times), not causes (high CPU). Set actionable thresholds that indicate genuine problems, not noise. On-call rotation ensures someone responds.

Dashboard design: create operational dashboards showing current system health, and analytical dashboards showing trends over time. Keep operational dashboards simple: green/red indicators for key services.

Performance budgets: set maximum thresholds for page weight, JavaScript bundle size, LCP, and API response times. Enforce budgets in CI/CD to catch regressions before they reach users.