Correlation ID

Thread a unique request ID through headers, logs, and downstream calls.

observe

Detailed Description

Correlation IDs are a lightweight observability baseline even before full tracing.

They let teams search logs from multiple services for one user request.

Gateway creates X-Request-ID
All services forward it
All logs include it

Pros

Simple and immediately useful

Cons

Must be propagated consistently

Examples: X-Request-ID, express-request-id, Morgan logger