Distributed Tracing

Problem 

One user request travels through:
API → Orders → Payment → Database → Queue
It takes 4 seconds. Which component consumed those 4 seconds?

Solution — Distributed Tracing

Propagate trace context across service boundaries. 
Trace 4711
├─ API       4.0s
├─ Orders    3.8s
├─ Payment   3.5s
└─ Database  0.1s
Core idea: tracing reconstructs one operation across distributed components.