What are the main types of metrics in Prometheus?

In Prometheus, the main metric types are:

• Counter: monotonically increasing, used for counting events (e.g., number of requests).
• Gauge: can increase and decrease, reflects the current value (e.g., CPU load).
• Histogram: collects the distribution of values over intervals, useful for measuring response times.
• Summary: similar to histogram but provides quantile estimates, such as the 95th percentile of latency.

Example of creating a counter in Go using the Prometheus library:

var requestCounter = prometheus.NewCounter(
    prometheus.CounterOpts{
        Name: "http_requests_total",
        Help: "Total number of HTTP requests",
    },
)

func handler(w http.ResponseWriter, r *http.Request) {
    requestCounter.Inc()
    // handle request
}