Part 4: Finding problems in large systems

So far, we’ve focused on diagnosing issues inside a single application. But in the real world, most systems are made up of many services, databases, and queues—all talking to each other across networks. In this environment, problems don’t just live in one place. They can hide in the gaps between services, in unexpected data mismatches, or in the way the system as a whole reacts under stress.

This part is about troubleshooting at system scale. We’ll learn how to uncover failures that happen only when services interact, how to measure and verify data consistency across boundaries, and how to trace multi-step operations that cross multiple components. We’ll also look at strategies for catching drift between systems before it becomes a serious outage.

By the end of this part, you’ll be equipped to investigate issues that span entire architectures—not just single apps—using the right combination of logs, traces, metrics, and detective work to keep complex systems healthy.