Metrics and Tracing

At the end of one test run, the health endpoint of the booking service reported a single word: UP. During the same few minutes, the service had confirmed three bookings, rejected one, and waited on the payment provider for every charge. None of that appeared in the health response, because health reports only the present moment. The log held it as scattered lines that someone would have to count by hand.

Facts like these need numbers recorded over time, and a slow request needs a record of where its time went. This lesson covers both