AWS X-Ray: Distributed Tracing

Modern cloud applications are rarely monolithic. A single user request might pass through an API Gateway, invoke a Lambda function, query DynamoDB, call an external API, and publish a message to SQS — all before returning a response. When something goes wrong (or goes slowly), pinpointing the bottleneck across these distributed components is extremely difficult with logs and metrics alone. This is where AWS X-Ray comes in.

---

What Is Distributed Tracing?

Distributed tracing is a technique for tracking a request as it moves through multiple services. A trace is a collection of segments (one per service) that together represent the full journey of a single request.

Think of a trace as a timeline:

[API Gateway] ──> [Lambda Function] ──> [DynamoDB]
   12 ms              85 ms               40 ms

By visualising this timeline, you can immediately see that the Lambda function accounts for most of the latency, and within that, the DynamoDB call accounts for nearly half.

---

Core Concepts

Traces

A trace is the top-level entity. It represents one end-to-end request and is identified by a unique Trace ID (e.g. 1-5e1a1234-abcdef1234567890abcdef12).

Segments