Can you list the main types of metrics used in Prometheus?

The main metric types in Prometheus are:

• Counter — a monotonically increasing value, such as the number of requests or errors.
• Gauge — a metric that can increase or decrease, such as current CPU load or number of active connections.
• Histogram — distribution of values over intervals (buckets), for example, request response times broken down by ranges.
• Summary — similar to Histogram but additionally provides quantile estimates (percentiles) for values.

Each type serves different purposes for monitoring and analyzing system performance.