Sleuth provided distributed tracing for Spring Boot microservices, tagging requests with trace and span IDs so a single transaction could be followed across service boundaries; it's been replaced by OpenTelemetry in Spring Boot 3.x.
Key Points: • Sleuth automatically added trace/span IDs to logs and propagated them across HTTP and messaging calls between services. • This made it possible to correlate log lines from multiple services back to a single originating request. • Spring Boot 3.x dropped Sleuth in favor of Micrometer Tracing combined with OpenTelemetry, which is a vendor-neutral observability standard. • OpenTelemetry covers tracing, metrics, and logging under one umbrella, exporting data to backends like Jaeger, Zipkin, or a commercial APM tool. • Migrating typically means replacing Sleuth dependencies with micrometer-tracing-bridge-otel and an OTLP exporter.
Example: In a checkout flow spanning an order service, payment service, and inventory service, tracing lets you see one trace ID stitching together every hop, immediately showing which service added the most latency to a slow request.
Interview Tip: A concise interview answer is:
"Sleuth used to add trace and span IDs so you could follow a request across microservices in logs and tracing tools. It's no longer supported in Spring Boot 3.x -- the replacement is OpenTelemetry, typically wired in through Micrometer Tracing, which gives the same distributed tracing capability plus a broader, vendor-neutral observability standard."