In control theory, observability is a measure of how well internal states of a system can be inferred from knowledge of its external outputs. In other words, it is the ability of a system to externalize internal state data, namely logs (verbose and text-based representations of system events), traces (data representing a specific event that occurred within the application), and metrics (a numeric representation of point-in-time data, such as counters and gauges; for example, CPU, RAM, and disk usage). These are referred to as the three pillars of observability, which are needed for monitoring and analyzing the whole system.
Refer to the following link for more information on the three pillars of observability: https://www.oreilly.com/library/view/distributed-systems-observability/9781492033431/ch04.html ...
