Frontend Monitoring

Frontend monitoring is essential for understanding application health, user experience, and identifying issues before they impact users.

Key Areas

Area	Purpose	Key Metrics
Error Tracking	Capture and diagnose errors	Error rate, stack traces, affected users
Real User Monitoring (RUM)	Measure actual user experience	Core Web Vitals, page load times
Synthetic Monitoring	Proactive testing	Uptime, response times
Logging	Debug and audit trail	Log volume, error patterns

Core Web Vitals

Google's Core Web Vitals are critical metrics that affect both UX and SEO:

Metric	Description	Good Threshold
LCP (Largest Contentful Paint)	Loading performance	< 2.5s
INP (Interaction to Next Paint)	Interactivity	< 200ms
CLS (Cumulative Layout Shift)	Visual stability	< 0.1

Four Golden Signals

Essential signals for monitoring any distributed system:

Signal	Description	Frontend Example
Latency	Time to complete requests	API response time, page load
Traffic	Amount of demand	Page views, API calls
Errors	Rate of failed requests	JS errors, failed fetches
Saturation	Resource utilization	Memory usage, CPU load

Monitoring Strategy

┌─────────────────────────────────────────────────────────────┐
│                    Frontend Monitoring                       │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐      │
│  │    Error     │  │     RUM      │  │  Synthetic   │      │
│  │   Tracking   │  │  Monitoring  │  │  Monitoring  │      │
│  │              │  │              │  │              │      │
│  │ • Exceptions │  │ • Web Vitals │  │ • Uptime     │      │
│  │ • Crashes    │  │ • Page Load  │  │ • Smoke Test │      │
│  │ • Breadcrumbs│  │ • User Flow  │  │ • Regression │      │
│  └──────────────┘  └──────────────┘  └──────────────┘      │
│         │                 │                 │               │
│         └─────────────────┼─────────────────┘               │
│                           ▼                                 │
│                  ┌──────────────┐                           │
│                  │   Alerting   │                           │
│                  │   & Alerts   │                           │
│                  └──────────────┘                           │
│                           │                                 │
│                           ▼                                 │
│                  ┌──────────────┐                           │
│                  │  Dashboards  │                           │
│                  │  & Reports   │                           │
│                  └──────────────┘                           │
└─────────────────────────────────────────────────────────────┘

Implementation Checklist

Set up error tracking (Sentry, Bugsnag, etc.)
Implement RUM for Core Web Vitals
Configure alerting thresholds
Create monitoring dashboards
Set up synthetic monitoring for critical paths
Document incident response procedures

Monitoring Overview