How can monitoring metrics be customized in Prometheus?

To customize monitoring metrics in Prometheus, you need to follow these steps:

1. In monitored applications, use Prometheus client libraries (such as Prometheus Java Client or Prometheus Go Client) to define and expose custom metrics. These client libraries offer basic types of metrics like Counter, Gauge, and Histogram, allowing you to choose the appropriate type based on your application’s needs.
2. Add a new job configuration in the Prometheus server’s configuration file (prometheus.yml) to instruct Prometheus to collect custom metrics from the application. Specify the application’s address and port in the configuration so that Prometheus can access the application’s metrics.
3. Restart the Prometheus server to load the new configuration.
4. In the Prometheus web interface, custom metrics can be queried and visualized using the query language PromQL. For example, one can use the sum() function in PromQL to calculate the total of a Counter type metric, or use the rate() function to calculate the rate of a Gauge type metric.

It is important to ensure that custom metrics adhere to Prometheus’ data model and specifications, so that Prometheus can properly parse and handle these metrics. Additionally, consideration should be given to naming metrics and using labels effectively in order to better organize and manage metric data.