Monitoring and logging form the visibility layer of modern infrastructure, enabling teams to understand system behavior, diagnose failures, and optimize performance. Observability—the ability to infer internal system state from external outputs—has emerged as the organizing principle, unifying metrics (quantitative measurements), logs (timestamped event records), and traces (request execution paths) into a coherent framework. Together, these three pillars provide the instrumentation necessary for running reliable, scalable systems in production. Effective monitoring requires balancing signal-to-noise ratio: collecting enough data to answer questions, but not so much that costs explode or teams drown in alerts. The shift from traditional monitoring to observability represents moving from "known unknowns" (predefined dashboards) to exploring "unknown unknowns" through high-cardinality data.