correlation ID
also: request ID, trace ID, request correlation ID, X-Correlation-ID
A unique identifier assigned to a request or transaction that allows you to track and correlate related log entries, messages, and events across multiple systems or services.
A correlation ID is a string or number generated at the start of a request that gets passed along and logged at every step of processing, enabling you to follow the complete lifecycle of that request through distributed systems.
In Linux systems and microservices architectures, correlation IDs are especially useful for troubleshooting. When a user reports an issue, you can use their correlation ID to grep through logs across multiple servers and services to see exactly what happened at each stage. For example, a web request might generate correlation ID req-12345-abc, which appears in your web server logs, database query logs, and cache service logs—all linked together.
Most modern application frameworks and logging systems support correlation ID propagation through HTTP headers (like X-Correlation-ID) or message queue metadata, making it standard practice in cloud-native and containerized Linux deployments.