- The RED method, introduced by Tom Wilkie in 2015, focuses on request-serving services by measuring Rate, Errors, and Duration from the caller's perspective to assess service health.
- The USE method, defined by Brendan Gregg in 2012, applies to resources like CPU, memory, and disk, evaluating Utilization, Saturation, and Errors to identify resource bottlenecks.
- RED and USE address different layers: RED is service-oriented and blind to resource issues, while USE is resource-oriented and ignores service-level performance, highlighting their complementary roles in observability.
- Linkerd provides automatic RED metrics for meshed pods via its proxy, emitting response_total and response_latency_ms_bucket metrics without application instrumentation, covering east-west traffic.
- In an example incident, RED metrics showed rising latency while USE metrics revealed pod-level CPU throttling, demonstrating the need for both methods to diagnose issues comprehensively.