The entire world does not (yet) revolve around Prometheus, nor provide Prometheus metrics out of the box. Exporters are tools that let you translate metrics from other systems into a format that Prometheus understands.
In Chapter 7 one of the first exporters you will probably use, the Node exporter, is covered in detail.
In Chapter 8 you will learn how Prometheus knows what to pull metrics from and how to do so.
Chapter 9 dives into monitoring of container technologies such as Docker and Kubernetes.
There are literally hundreds of exporters in the Prometheus ecosystem. Chapter 10 shows you how to use various typical exporters.
As you may already have another metric-based monitoring system, Chapter 11 looks at how you can integrate those into Prometheus.
Exporters don’t appear from thin air. If the exporter you want doesn’t exist, you can use Chapter 12 to create one.