Prometheus — what is it, how is it used, how does it work, how does it collect metrics, what are the main types of metrics?

Prometheus is an open-source monitoring and alerting system focused on collecting and storing metrics in a time-series format.

How it works:

• Prometheus periodically scrapes HTTP endpoints that expose metrics in a specific format.
• Metrics are collected as key-value pairs with timestamps.
• Data is stored in a local time-series database with scalability options.

How it collects metrics:

• Applications or services expose metrics via HTTP in Prometheus exposition format.
• Prometheus makes scheduled HTTP requests to these endpoints and collects data.

Main types of metrics:

• Counter — a monotonically increasing counter (e.g., number of requests).
• Gauge — a value that can go up or down (e.g., current CPU load).
• Histogram — distribution of values over intervals (e.g., response time).
• Summary — similar to Histogram but with quantiles.

Example in C#:

using Prometheus;

var counter = Metrics.CreateCounter("myapp_requests_total", "Total number of requests.");

// In request handler
counter.Inc();

Then Prometheus will collect the myapp_requests_total metric from your application.

In commercial projects, Prometheus is often used for monitoring performance, service availability, and user behavior analysis.