Metrics & Instrumentation
Practice this topic in a realistic system design interview
Suppose you run an online store. One evening, the checkout page starts getting slower. At first, only a few requests are affected. Then more.
Without metrics, the first sign of trouble might be a flood of customer complaints.
With metrics, the picture is different. A graph shows checkout latency climbing from 200 ms to 2 seconds over the past 15 minutes. Another graph shows the database connection pool is almost full. An alert fires before most customers notice.
Metrics give you a continuous, numeric view of how your system is behaving. They tell you whether things are normal, when they stopped being normal, and which part of the system changed.
In this chapter, we will learn what metrics are, the main types of metrics, what you should measure in a system, and how applications are instrumented so those metrics can be collected, stored, and used for dashboards and alerts.