Distributed Tracing Explained
A trace is a tree of spans, and the tree only exists because every service forwards the same identifiers. We follow a request as it crosses service boundaries: the trace ID, the span ID, and the parent span ID travel in headers, and each service appends its own node to the tree.
Topics covered:
- The data model: trace ID, span IDs, and parent-child edges
- Context propagation: the W3C traceparent headers that carry the tree
- Where spans get created: client, server, and internal spans
- Timing: how the critical path is computed from span durations
- Sampling: why head sampling loses trees and how tail sampling keeps them
- Storage and query: reconstructing one trace from millions of spans
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