Application Monitoring and Observability

Monitoring: Keeping an Eye on Your Application

Monitoring is how you know what's happening with your application. When everything is working, monitoring tells you that. When something goes wrong, monitoring tells you what, when, and why. Without monitoring, you're flying blind — you only find out about problems when users complain.

The Three Pillars of Observability

Observability is built on three types of data. Metrics are numerical measurements over time — how many requests per second, what's the error rate, how much memory is being used. Logs are records of events — each request, each error, each significant action. Traces follow a single request as it travels through multiple services, showing where time is spent.

Each type of data answers different questions. Metrics tell you something is wrong. Logs tell you what happened. Traces tell you where it happened. Together, they give you a complete picture of your system's health.

Metrics: The Health Dashboard

The most important metrics to track are the four golden signals: latency (how long requests take), traffic (how many requests you're handling), errors (how many requests fail), and saturation (how close your resources are to capacity). These give you a quick overview of system health.

Prometheus is the most popular tool for collecting metrics, and Grafana is the standard for visualizing them. You set up exporters that collect metrics from your servers, databases, and applications, and Prometheus scrapes them at regular intervals. Grafana turns this data into dashboards and alerts.

Logs: The Record of Everything

Logs are where you look when something goes wrong. Every significant event in your application should produce a log entry with a timestamp, severity level, and enough context to understand what happened. Structured logging — where logs are JSON objects with well-defined fields — makes them searchable and analyzable.

The ELK stack (Elasticsearch, Logstash, Kibana) is the most common log management system. Logstash collects and processes logs, Elasticsearch indexes them for fast searching, and Kibana provides a UI for exploring them. A simpler alternative is Loki, which works with Grafana and is easier to set up.

Alerts: Knowing When to Wake Up

The purpose of monitoring is to alert you when something needs attention. But not every anomaly needs to wake someone up at 3 AM. Define alert rules carefully: high error rate, high latency, low disk space, certificate expiring soon. Each alert should have a clear description of what's wrong and how to fix it. Too many alerts lead to alert fatigue, where people ignore them.

Real User Monitoring

Server metrics tell you about your infrastructure, but they don't tell you what your users are actually experiencing. Real User Monitoring (RUM) collects data from the user's browser — page load times, interaction delays, JavaScript errors. Services like Google's Chrome User Experience Report and commercial tools like Datadog RUM give you visibility into the user experience as it actually happens.