Why Modern Apps Need Observability: A Guide to the LGTM Stack

Observability is the ability to understand a system's internal state purely from its outputs — including logs, metrics, and traces — without redeploying or manually investigating. Unlike traditional monitoring, which only catches known failure modes through pre-set alerts, observability enables engineers to investigate unexpected issues after the fact. The LGTM stack — comprising Loki for log aggregation, Grafana for visualization, Tempo for distributed tracing, and Mimir for scalable metrics — is an open-source toolset designed to deliver full observability in one pipeline. OpenTelemetry acts as the instrumentation standard, with the OTel Collector serving as the central data routing layer across all four tools. Together, these components allow engineering teams to reconstruct exactly what happened during an incident, including root cause and timeline, even hours after the fact.